“Went insane” doesn’t even carry a meaning in this situation for fuck’s sake.
Psychology barely existed in the 1870s– I mean, we’re talking about before Freud’s career had really started– and what there was of it was often worse than nothing. What was said about him at the time doesn’t necessarily bear any relation at all to reality or to what we’d consider mental illness nowadays. And we certainly can’t accurately diagnose someone across more than 100 years.
We don’t know what was going on in his head. All we know is what he did. We don’t know if he threatened and eventually committed violence because he was traumatized and haunted and couldn’t cope, or whether it was deliberately calculated to terrorize and control the people around him because he just wanted to be in control. We. Don’t. Know.
And you can debate whether it should be called mental illness in both of those cases, for that matter.
“Went insane” doesn’t mean anything about his mind. We don’t know anything about his mind. People are saying it, in this situation, to mean “did something scary and I don’t understand why.”
Which has no relation to whether someone has an actual mental illness.
Mental illness does not equal violence. Please don’t do the thing.
I guess “but he went insane in real life” sounds like a catchy excuse. “But he started abusing her in real life” doesn’t sound as good for justifying playing the character that way in roleplay, i.e. talking that way to real people.
So, I have two problems with this as an explanation:
1. I care less about “but my character is chaotic evil!” than about whether you’re causing people harm in real life.
2. Don’t say “went insane” when you mean “hurt someone”.