The letter writer appears to be that's 18 and is expressing concern for their dad:
Q: Dad-Related Dilemma: My mom left my dad for another man 10 years ago, when my brother and I were in grade school. She took us with her, and the loss of his family turned my father into a bitter man. He now considers himself a men's rights activist. From what I can tell, the men's rights movement my dad belongs to believes that American law and society has institutionalized misandry. One website my dad frequents warns men not to date single mothers because their children might accuse the boyfriend of molesting them to reap the benefits of victimhood. My dad speaks often about the men's rights movement, and when my brother and I don't want to listen, he accuses us of being brainwashed by feminists. His behavior doesn't come across as crazy so much as it does misogynistic. Now I'm 18 and could stop seeing him if I wanted to. But my brother is younger and still has to see him. My mom doesn't know the full story because we don't want her to overreact. What should we do?
A: Your mother leaving him may have caused your father's personality change—it may also be that his personality was in place and your mother couldn't take it anymore. Both you and your brother are old enough to have some direct discussions with your father about your relationship with him. Talk to your brother and see if he wants to join in such a conversation, and if he doesn't, make some time alone with your father. He needs to be told that his activism is his business, but you don't want to be his audience anymore. Say that you both understand he has strong feelings about women and the legal system, but being lectured to is poisoning your relationship. Reassure him that you love him and want to spend time with him, but you want to talk about things that are less painful and volatile. If he won't curb his enthusiasm, then you can start peeling off from your visits. Now that you're 18, spending less time with your father would be bound to happen anyway. But if you do that, be a sounding board for your brother on how to deal with Dad's ugly obsession.
Okay first things first. Personally I think this dad got hurt. Hurt real bad. How can you not be hurt real bad after having your wife leave you for another man? And after being hurt he simply didn't have the system of support a lot of men are not offered because of the idea that men don't need it (and often don't take when offered it for that same reason). No matter how toxic he may have become over those 10 years the problem isn't the misogyny or hatred of feminists. Those are just a gun so to speak. A convenient weapon to take up after not having a proper outlet for his pain, which led him to wanting to take up a weapon to lash out with. I think that's the basis for a lot of MRAs (versus the belief that MRAs exist only to hurt feminists and women) and I think his chances would have been a lot better if he had fallen in with some MRAs that weren't so poisoned (yes they actually exist).
I think that if this 18 year old and little brother wanted to (and I don't think they should feel obligated) they could do a lot of good in healing his pain by showing that they love him. Unless this dad abused mom or something else to actually run her off she did him wrong plain and simple. More than likely the dad having anything resembling a relationship with the mom at this point is a totally lost cause, but its not a lost cause for the kids.
One other thing that bothers me is the Prudence calling it an "ugly obsession". Okay for the little bit that MRAs get mentioned in the media it usually negatively and its not always justified frankly. So I'm wondering if she's talking about his poisoned attitude or identifying as an MRA in general. (I sent her an email asking for context on that, I'll post if I get a reply.)
Mind you I don't know any details beyond that letter but with the way the letter writer sounds it seems like he changed after mom left (and I almost think Prudence is trying to bury that with the "may"s in the start of her response). Just like all movements there are good elements and bad elements. It seems like he has fallen with a bad element.