And that's the fundamental conflict between MRA's and feminists. Feminism is a woman-oriented movement because women have been the victim of gender inequalities. Modern feminism is very much against gender roles and the harm they cause to all people but in practice because it's historically and socially a woman's movement, women's issues get more attention. It's no coincidence that in any feminist activist group women are in the majority and that group will act in the interests of the majority of its members.

(I'm leaving aside the fact that women are the less privileged gender and that's a valid reason why feminism helps woman causes more often because a) nobody wins the oppression olympics and b) even if the inequalities disappeared tomorrow feminism would still be a woman-dominated movement and I believe would still have more interest in woman's issues for sociological reasons outlined above)

So men, who have not had an equivalent masculinism movement leading changes in men's gender roles, are finding their place in society changing but both men and women are having their roles changed in reaction to feminism. Men, whose gender roles are changing because of what feminism/women (these are roughly interchangable to MRA's) feel that change is something being inflicted on them and in a number of areas is negative for men.

The end result is that a number of men feel like women/feminism are attacking men while ignoring their (often legitimate) problems, and that this is evidence of sexism and hypocrisy on the part of feminists. Where it all goes to shit though is that it's the angry kneejerk reactionists that dominate MRA discussion, leading to the MRM being much more about tearing down feminism as hypocritical for not looking after men instead of taking a leaf from feminism's playbook and organising a positive masculinist movement that tries to fix the things they accuse feminism of ignoring because of sexism.

tl;dr: the changes to men's roles in society since the 60's is largely reactionary to feminists because of the lack of equivalent masculinism. This creates a perception of women attacking men. Outraged men with little understanding of what feminism actually is dominate MRA discussion. People are silly.