I don’t believe children become violent, aggressive or incredibly reckless for no reason. I believe it is usually due to trauma or neglect/ lack of positive attention even (or especially) in ND children.
...often down to neglect and lack of support and love at home.
it’s hard not to notice that it’s often the children who have unstable home lives, multiple younger siblings and no boundaries or routine.
I think you're conflating several things here.
Unstable home life, multiple (half) siblings, no boundaries/routine is a common pattern where parents are struggling, likely due to a combination of (at least 2 of) poor executive functioning (ie, difficulty considering future effects of current actions), and/or other physical or mental health difficulties, and/or their own trauma, and/or lack of good modelling from their own parents. It is very difficult to offer support to these families, I've talked to people on here about this before. You occasionally see someone in one of these holes posting desparately but it is very difficult to get them to actually make any changes, because when someone is living in this kind of chaos, the effects of all the difficulties sort of "lean on" each other and make everything else heavy and even if you make progress in one area it tends to collapse very shortly under the weight of the others, unless there is sustained and robust support AND the root cause of the executive functioning/other health issues are identified and addressed. This is generally not how any outside support actually works, support organisations are set up to come in, offer advice/structural support for a short time and then take the support away, and it doesn't work or the effects are only very temporary. The effects of this kind of chaotic lifestyle ripple outwards and are very damaging.
But in any case adults being stuck in this kind of cycle doesn't mean they don't love or care for their children. Often they do but they are overwhelmed.
I've been there, in my case the chaotic parts of my home life with DS1 were caused by undiagnosed/unmanaged ADHD, and generational trauma - this is a weird one because my own childhood was happy. I would not describe it as traumatic, my parents did split up, I was bullied at school, and my mum has told me of some parenting that my dad did which upset her but overall I don't consider that I have childhood trauma. Maybe some "little t trauma" (which I think everyone has to some extent and is not really what I'm talking about). But my mum has significant trauma and so does my dad. I didn't even know this until I was much older but I do think that the ways their trauma affected them affected me in turn and not even in ways I could put my finger on. It's not their fault, and I don't blame them for it but I'm (still!) frequently surprised when I realise the differences between my own upbringing and what to me feels like a more "normal" upbringing. But I assumed my own life was normal as I was going through it - everyone does, I think.
Yes I can see the link between the difficulties I had maintaining structure and calmness at home and my eldest's difficult behaviour (though he's not that extreme now) and I can see how having my own ADHD better managed, and having more structure day to day leads to much better and more manageable behaviour in my younger two DC, and YY particularly in DS2 who also has ADHD and possibly ASD. I do think this is really important, I want to write something about it esp the things which have worked for me, as a lot of "standard" advice, as written, missed the mark.
But some other things I think also play in.
I notice at least on MN/other forums there is a widespread belief that violence/aggression are unnatural behaviours, and so if children are using them, they must have seen them somewhere to copy them. I do not think this is the case. It can be true for certain kinds of behaviour, for example vocabulary is not innate, it is learnt although it can be picked up anywhere at all and once DC have learnt that a word has more power they will store that knowledge, whether it means that they feel afraid of it, or it comes out in moments that they feel under threat. But violence and aggression in general are instinctive defensive behaviours in humans, just as they are in animals. If you've ever seen a tiny kitten or small dog square up and hiss/growl/yap at something much bigger, you've seen this in action. Those are aggressive behaviours, but they are primarily a fear/stress response, part of the fight/flight/freeze pathway.
Violence is also one of the the most primitive communication methods that we have, and aggressive body language or verbal aggression is universally understood as a precursor to violence. It is so primitive that it works across species. We understand signs of aggression in animals and they in us. Even when humans lose other brain functions (such as in dementia, TBI or intellectual disability) violence/aggression remains, sometimes without the safeguards that people with full brain function have.
When people of any age do not have access to sufficient language or other social skills, either because they have not developed them for whatever reason or they are temporarily unable to access them due to something like a strong emotion, or they have tried using these ineffectively, they may fall back on violence because the intent of communication is usually pretty clear (often: back off, or leave me alone, stop that/do not do that again, or give me that thing that you have) and it tends to work, even if you experience consequences as a result. (The other fallback is avoidance).
Most children over time develop sufficient communication and social skills and emotional regulation and impulse control that they are able to successfully access a number of other ways to handle almost any situation, and can run through several in turn and not get down to the lowest form of communication which is violence (preceded by verbal/physical aggression). This combined with the fact that violence/aggression carries a fairly clear social penalty discourages the use of violence and aggression except in extremis. But some children either grow up in an environment where the use of violence and aggression is normalised and modelled by adults, or is inadvertantly rewarded (e.g. by parents giving in to tantrums), and/or, they do not for whatever reason develop alternative skills for communication/conflict resolution/acceptance of difficult situations and emotions.
The lack of development could be related to environmental factors such as lack of appropriate adult attention or opportunity to practice said skills, e.g. when child has excessive screen time. But these can also be related to a ND or other difficulty. Hearing difficulties can affect speech, for example. Sensory processing differences or learning difficulties can massively increase a child's cognitive load. And very often you find there is a cyclical effect, where children struggle to communicate with peers or adults outside the family or manage a certain situation, so they stop trying, or fall back on strategies which are at least effective (aggression/avoidance). Or adults become stressed and do not know how to handle their child's behaviour and start to avoid things like playdates and/or fall back on more screen time, perhaps not even consciously!
Support in the UK for this kind of early difficulty BTW is shit. Truly truly inadequate. Most often to start out with, you get completely inappropriate advice based on consequences, which will do fuck all if the child doesn't actually have access to other options to run through. It's like the first assumption is that the parents have encouraged the behaviour by giving in to tantrums, but even if this is the case, children benefit much more from support with communication/social/emotional skills than they do from being punished for falling back on something which generally works anyway. And being punished for something you don't actually have the skills to manage another way increases stress and damages the parent-child relationship, which will increase stress behaviours.
Secondly you're told to hang on because the child will grow out of it. Which they might. Many do. But if they don't then again usually the first thing you're told is consequences. Which, again, does not help if they don't have anything else to fall back on. Or sometimes, often alternative parenting advice reverts to lowering/reducing demands, which can be useful as a temporary stress reduction overall to allow children space to develop skills - but avoiding everything means children have less opportunity to practice more adaptive skills, so "low demand" or "they are only little" can backfire as well.
Or sometimes a child is not violent/aggressive when they are younger because they do have just enough of the helpful skills or can use avoidance instead and it's only when they are older and expectations of them increase past what they actually can manage to compensate for, that you find aggressive or defiant type behaviours show their face. But again, first port of call = consequences. And with older children, it's often assumed that if consequences don't work then increasing the consequence will, which is not evidence based at all, in fact the evidence shows that mild consequences are just as effective as severe ones, and the overall effectiveness of consequences is "not very, and only in conjunction with rewarding/development of positive replacement behaviours".
And if parents need to take responsibility I think we also need to be looking at schools taking responsibility - why are schools so stressful and difficult for many ND children to manage? What about the health system and social services - why is it so difficult for parents to access good quality advice and support with DC's development and behaviour, early and consistently?
We need to look at corporations taking responsibility - why are screens so much more addictive and prevalent these days with little to no attempt to protect DC from these effects? UPFs marketed directly to children? Relentless pursual of profit by companies/work culture/cost of living taking parents away from DC at home?
I could go on but we are still on summer holidays so I need to take my DC out and spend time with them 
But in short, it is much more complicated. It is not as simple as "parents need to take responsibility" often they are already doing the best they can with the knowledge and resources (emotional, practical) they have access to and anyway how does pointing the finger even help? Whatever happened in the past is already done.
And a final thought:
I think a lot of parents would LIKE to take responsibility in terms of being able to access resources (information, assessments, therapy, advice, courses, appropriate schools) which would actually help their DC, but do not find these kinds of things available.