@Hoplolly its not just the first wives on (although many SMs are also first wives - both in the sense that they may have been married before and they may be their husband’s first wife, even if he had children with someone else - which probably upsets the anti-SM contingent more).
It’s also the former SC who blame their SM for their parents’ choices, and cannot bring themselves to believe anything that might make them reassess ghat position.
And the entitled parents who think a ‘partner’ means someone to delegate your responsibilities to. These posters generally insist their partner would be put on his ear if he didn’t provide the expected services and that he’s an equal partner - but, ultimately, the equality wouldn’t extend to making decisions about anything the poster disagreed with. These posters are horrified at the idea a SM might have boundaries and expect parents to parent their children.
And the people who generally want to maintain the idea that SMs are awful in multiple ways.
The fact is that some men do behave in the ways that OP describes. Although I think those men believe that love comes with obligations to provide domestic labour (just as the entitled mothers insist that any partner of theirs must take on the aspects of their parental responsibility that suit them). These parents tend to have a weirdly transactional view of love and partnership. My STBXH is one of these - I remember him angrily telling me there was ‘no point’ in a relationship if I wasn’t going to do childcare for his children so he could go to the gym etc (the etc being many, many things).
These, sadly, are the kind of men at bottom of so many of the problems shared on this board. But, they’re also the men at the bottom of so many of the non-step family problems on AIBU or relationships. These men are a subset of men that are always going to be over represented on MN threads because they so often are the problem. The father who stars in the current eating all his son’s Easter chocolate thread, for example, would be a shit in any context. If that OP divorces him, he’ll likely be a self and entitled prick in any future relationship.
I don’t really understand why people get so angry at women, especially SMs, when the issue is a specific man who is behaving badly.