My experience, as a mum of 7 year old with autism and ADHD (and who is CONSTANTLY having battles with his teachers) is that MOST parents are good and concerned and caring, just as MOST teachers are.
I'd say the proportion of parents who don't give a shit and do the right thing is slightly higher than the proportion of teachers, as if you really hate kids, you'd go for a less stressful job.
I am probably considered quite a challenging parent, as I am happy to back up the school but they have to have done right by my son and his special needs first. I will accept and back any punishments they give, but will expect them to also be reflective about their own actions.
However, many parents refuse to back up the school and will even claim CCTV evidence is fruadulent. These are also the parents who complain when their child doesn't get any GCSEs and blames the school.
I agree that parents and schools need to work closer together though. However, IME it is very very hard to get parents of the most extremely disaffected children involved. You can write, phone, text, do home visits and they still won't/ can't get their child to come to school or be polite/civil. Any events for parents are well attended by the parents who already work well with the school. I think that most schools reach out their hands very far towards all parents and even further towards those facing challenging times. But it's about time some parents reached a hand out back.
If you have kids, you can't just abdicate all responsibility when they start school. Most parents still stay involved up to Junior school, perhaps, but then drift off.
It is very very annoying when you are trying to educate a child (in all senses, ie social skills etc., to prepare them for later life) when most teens who I teach say that school is son much stricter than home "because there are all these consequences and punishments and rules and stuff". Some genuinely have no boundaries at home and then they're screwed at school and when they start work as they won't accept anything.
Then there's the parents who let their daughters (some as young as 12) out on a Friday night and don't care what time they're back and don't have any idea that they've spent the evening drinking and taking drugs, too out-of-it to notice that the boys are taking turns on them without condoms and filming it . And the parents who equally don't seem to worry about where their sons who are doing this are. This isn't a one off. We keep hearing "well, I can't stop him going out/ drinking/ truanting" and I think it's so so sad. Parents do need support but they also need to make an effort. As do teachers. But most of the most injurious behaviour is out of school and parents need to be aware of that.