Actually, they come from the traditional family where one partner, usually the woman, would be at home and keep things tidy + care for children, and the other partner, usually the man, would work. In such a relationship the partner who stayed at home is obviously disadvantaged when it comes to the situation after a divorce, because the other partner spent most of the time during the marriage building the skills in whatever they work in, creating contacts at work and building a career while you spent your time supporting them, and creating an environment where that partner can focus on their work as much as possible. For that reason, alimony laws are not gendered in principle, a well-earning woman also has to support her stay-at-home ex-husband for the same reasons, it's just a much less common case. I can't say that I'm too well-read in the MRA movement, but the ones I stumbled on during discussions very much acknowledge that the dynamic of "Women were seen as needing protection, thereby men were forced to take on the role of the protector." exists, and from an evolutionary perspective, it is perfectly sound, too. They just don't accept it as the "Gotcha!" that you try to turn it into, and I have to say I very much agree that it's a non-argument. Because even if we assume that every case of discrimination against men originally stemmed from discrimination against women, it is still the case that discrimination against men now stands on its own. Just fighting against discrimination of women does not on its own remove discrimination against men, that's just a flawed conclusion that so many third wave feminists try to push. Men's issues need to be tackled directly.