People often use the metaphor of the pendulum when they talk about social change, particularly with respect to such things as civil rights. I've always detested that metaphor, because we don't want to oscillate between extremes; we want to move to a nice, fair equilibrium where everyone's rights are respected, and stay there. And while gravity can be trusted to push a pendulum towards that center, momentum will always cause it to overshoot. With a pendulum, the right thing to do (if you want to end up stable at the center) is to apply force in the opposite direction of whichever way it's going, to drain its momentum so eventually it comes to rest. If social justice really were like a pendulum, then we all should have been pushing against Martin Luther King Jr. and the civil rights movement, not to oppose it per se but to help slow it down so it would come to rest at the happy medium.
But we now recognize that the "moderates" who urged Dr. King to be patient, not to move so fast, were simply wrong. Even if there is a force of gravity gently tugging us in the general direction of social equality, the pendulum here is mounted on a rigid and far from frictionless pivot, and can quite easily remain at a socially unjust status quo indefinitely. We have to push it to get it to budge, and historically we've had to push pretty damned hard, because there's always someone trying to keep it right where it is.
(Also, the pendulum metaphor misleadingly suggests that there's symmetry in the distribution of injustices over time, and sure, we may be on top right now, but it all evens out because remember when white Europeans were slaves of African overlords, or when a man's legal personhood was subsumed under that of his wife? Me neither, but it must have happened because pendulum!)
Lately we have been hearing about the Men's Rights movement, whose position seems to be that the pendulum has swung too far and now men are disadvantaged as women once were. I have mixed feelings about this. On the one hand, yeah, there are situations in which men suffer injustices simply because they are men, and so yeah, I sympathize. I've had to contend with various inconveniences for being a man myself.
But on the other hand, I'm very much aware of how many advantages I enjoy simply by virtue of being a man in this society, how easy it is to take them for granted, and how much I probably enjoy without even noticing. On the balance, it's pretty obvious to me that I come out ahead on the deal, overall, and so I feel it would be undignified for me to complain about the times it works against me.
I would call it unmanly, but there is nothing uniquely masculine about courageously enduring hardships.
One of the minor ways being a man has occasionally disadvantaged me is when it comes to discussing feminism. I recall conversations in which my views were enthusiastically embraced as sensitive and enlightened until I happened to disagree over some point or other, when I suddenly became unqualified to know what I was talking about. (Gee, thanks for the object lesson in what it feels like to be marginalized, but wouldn't it be more helpful to model for me how to respect someone as an equal?) My gender shouldn't have any bearing on the validity of my arguments, but to some people it does.
Fortunately, as a man, I am qualified to say things about the Men's Rights movement without having to face such challenges, and the main criticism I have is actually the very same one I have of the term "feminism": it's adversarial and divisive. Feminism should not have been, and ideally isn't, about women's issues, but about addressing the impact of gender on human issues. That we call this movement "feminism" is a historical artifact of the fact that the bulk of the political and economic injustices resulting from sexism have been and still are borne by females.
So while I object a bit to the term "feminism", there's at least some justification for having focused on women's rights, particularly when they weren't thought to have any. I grit my teeth a bit every time I use the word, but that's the word we have. There is no such justification for creating a separate-but-equal masculism (packaged with a tastefully rugged blue label: "Feminism -- For Him!") to focus arbitrarily on gender injustice when it happens to disadvantage someone with a penis. Gender injustice is wrong whomever it happens to.
I sometimes use "Mankind" as a gender-neutral, inclusive term for our whole species. I figure I should be man enough to call myself a feminist in the same spirit.