I would say that men should be feminists because ultimately, it will lead to better relationships with the men and women in their lives, so happier lives for them and a fairer more just society for everyone.
They will have to give up their privilege and that is uncomfortable and unpleasant, but the long term benefits of living in a more just society outweigh the short term unpleasantness of giving up your privilege, although many white South Africans wouldn't agree with me.
I think you just need to look at the divorce rate to see just how unhappy the patriarchal model of men and women's interaction makes them. We need to develop a different model which ensures that both partners can be happy together. It's not a coincidence that married men are the happiest group and single women are happier than married women; nor that women are more likely to initiate relationship break-up, than are men.
The other thing about feminism, is that it would allow new parameters for masculinity. At the moment, men and women are socialised into roles that they might not choose if given more of a range of choices. I think men feel an enormous weight of expectation upon them and popular culture only serves to underline that. If you look at the media, Hollywood etc., the way men are portrayed is absolutely fucking ridiculous. They are practically God like. When they're punched in the face, they don't register the sheer pain of it as they would do in real life, they simply don't notice it as they merrily punch back and annihilate all their opponents. When they are challenged by the women in their lives, they rise to the challenge easily and are immediately forgiven for whatever outrageous behaviour they are being challenged on (I've just been to see Tooth Fairy
). When they assert their boundaries, as they do often, unlike men in RL who have to interact with other people who may not be bit-players to their lives, people notice and respect it and don't try and breach their boundaries anymore. This vision of masculinity is an absolutely impossible one to achieve and yet men have this template which is really aggressively pushed and which sets them up to feel failures IMO. A feminist society would do away with all that aggressive masculinity and just allow men to be men - whatever version of it whcih suits them, not some pre-determined role.
Robert Jensen is good on this, it might be useful: