Nothing is "entirely". Of course there are some benefits to men. I am stating an extreme view in part as a response to what I see is the one sided discourse that dominates the subject. Common discourse would have us believe that equality benefits everyone and harms no one. This is obviously nonsense. The power given to women by equality is (largely) power taken from men. We shouldn't pretend this is not the case. A more honest argument would acknowledge that giving women equal rights involves lowering the power of men, but that it's nevertheless the right thing to do.
There is a similar dishonesty that surrounds the gay marriage debate. Advocates of gay marriage (I am in favour in case there's any doubt) often say that heterosexuals don't lose anything by supporting gay marriage. I think that is simply not true. Heterosexual couples do lose something when gay marriage is recognised. They lose the privileged position that their family structure has traditionally enjoyed. That's a hell of a lot to lose actually! An honest argument would acknowledge that loss but would argue that it's the right thing to do anyway and that society will find new ways of structuring itself.
People who really understand the implications of equality, like Germaine Greer and Norman Mailer, know that it necessarily involves losers as well as winners. Equality is not a slight adjustment it is a revolution.
Pretending that women's rights and gay rights is an unqualified good for everyone is dishonest. There are losses as well as gains an honest discussion should be open to exploring these.