I think that the root of masculinism is a direct assault on feminism.
It was initiated by men who felt that they were as limited by society and needed a movement to compensate for that. It was saying that men are as vulnerable as women. I don't think there is an active movement -- more like a few individuals who promote this idea, hence the many definitions.
Also, I think that it is entirely a reactionary movement -- therefore doesn't leave much space for positive change. There are other men's movement people -- John Stoltenberg, check out Rebecca Walker's anthology "What Makes A Man" that are legitimately making change for men.