@merrymouse
The effects on other people of those ideas or policies being for other people to consider and advocate for.
And why wouldn't they - aren't they best placed to advocate for their own rights? That doesn't mean any group should disregard other people's rights.
I'm not suggesting that a men's rights organisation needs to be going out and lobbying for women's rights issues, for example.
But if they are going to lobby for a particular right for men, because having thought about it they think it would be good for them or solve some problem men have, they need to be considering what the wider effects of that policy would be. If it would mean more children in poverty for example, or less recourse for domestic abuse, or create bias in career hiring, that's a problem and they maybe should consider that their idea is unfair, however good it is for men as a group.
Even at a theoretical level, I am all for isolating ideas for thought experiments, even disturbing ones, but when you do that and someone says "actually, if we accept this idea about men, it would imply (some awful thing) about women and are we really willing to say that, even if it seems right when we are only thinking about men" - that's an important point. And not only in terms of fairness but in terms of gaining true understanding. It points to a problem that has been missed somehow in the thought process.
It's very rare that you can isolate a phenomena and analyse it without reference to the larger landscape without creating errors. Usually you even need some expertise about other system elements to get it right. Maybe that's the whole problem with the identity politics approach, it silos things to the point where the information results of analysis are warped.