I don't think this is a nominal question. I think it's particularly complex, and usually relates to the abuser having some form of personality disorder (usually NPD). I'm not suggesting this is an excuse for their behaviour, but it is a reason to explain some of it. Its easier for victims of the abuse (myself included) to assume they did and do everything with the sheer intention to cause pain and upset etc, and is most times a great survival skill to do this as sometimes trying to understand an abusers behaviour leans more towards trying to justify it to yourself. I did that for years and will never be doing it again.
That being said, from an objective point of view, looking at this on a biological and genetic human level, I do not believe that for every abuser, every single thing they do is done with malicious intent. Particularly for NPD, they are always deeply, deeply insecure, and their facade of grandiose is an unhealthy survival strategy to cope with this. Another common factor is trauma during childhood, or even just inconsistent/poor parenting. This can leave them with a lack of identity, lack of security and emotional attachment. This all builds up to them involuntarily creating this illusion that they are greater than everybody else. They do things that are harmful to others, while genuinely believing that they are doing what is right by the person, because they are genuinely so delusional that they cannot see it any other way.
However, the key to my point is that even when abusers who act abusively think theyre doing the right thing or whatever, they still know it is causing harm to the other person. They still know they are making their life a living hell. They just do not care whatsoever. To them, you dont really matter. You may as well be a dog to them, as youre just expected to jump through their hoops and be grateful to have them. And if you misbehave, you get punished and its deserved. Its disgusting.
I know from experience from having a lot of talks and arguments with my ex who was and still is extremely narcisstic. I think he knew what he was doing was wrong a lot of the time, but could not get past that he would not accept that certain (normal) behaviour (exhibited by me) was beneath him, and to him, this justified his actions. To any sane person, it definitely did not. Did he still know that he was deeply upsetting and depressing me? Yes. Did he care? No.
On the flip side, I think a lot of people who are abusive (including those without personality disorders), know exactly what they are doing. I genuinely believe that they are just so angry, self-absorbed and vile that they quite enjoy having a puppet as a partner. It is often times learnt behavior by their parents/relatives, and struggle to be any different because of this. I think this can (and more often than not) does overlap with personality disorders, which is why its exhausting to try and figure out whether they do it with intent or not. I believe that most of the time its a complex mix of both.
Ultimately I think all abusers know what they are doing is wrong, but a lot of them most of the time genuinely dont recognise what they are doing as abusive due to their own delusion, caused by an array of complex factors. When they do know its abusive, they do not care, or else they wouldnt be abusing you.
Please note I was in no way trying to justify abusive behaviour by anybody here, and those that are abusive hold the responsibility to get help for it - but they won't, because they don't think theyre in the wrong.
Side note to add: a lot of talk about victims of abuse being abusive in retaliation. This happens a lot, and does not inherently make them an abuser, too. Reactive abuse is just that, a reaction. You poke a bear, its going to react. It is ultimately a form of self-defence.
It is so deeply different than someone who is so mentally fucked up that they actively abuse somebody due to a PD, trauma, whatever fucking reason. Please do not try to bunch the two together.