He let it get to that point. There's no indication of an attempt to intervene with mental health professionals. This was a clearly troubled kid. I have no patience for parents who let their kids go off the deep end and then wipe their hands off and walk away.
I have a friend who's alive today because his working class parents made the wrenching decision to have him institutionalized when he was 17 because the knew something was wrong. He was violent, angry and self-destructive. They were NOT educated people, but they loved him enough to do what they could to save him. It's not his favorite memory, but he freely admits he would have been dead otherwise. He's lived a good life since then. They could have just kicked him out and washed their hands of him. At the same time, I know a family of educated professionals who shoved their son's burgeoning mental illness under the rug and ignored it for 30 years. He's never held a job for longer than a month (and doesn't work at all now) and is entirely reliant on them for everything. When his parents die, he will have no way of surviving and no mental health care to help him cope. He's an intelligent man, but crippled by the inaction of his parents when it would have mattered most.
I think the LW's father falls into that "passive parenting" category. She was lashing out over an extended period, but he apparently couldn't be bothered to really work on getting to the root of the problem before the situation escalated to one he deemed intolerable.
Now maybe the LW has totally mischaracterized the entire scenario, but the letter struck me as pretty honest.
I thought of the "wedding money" issue, but it's easy enough to turn something like that down if that's the ulterior motive. Weddings are also times when people reflect and reach out. I have a friend who did that - used his wedding as a moment to reach out to his father who had walked out on him 10 years before.