When you're talking about gender discrimination, you're including EVERYONE of that gender. Black, white, Japanese, Indian, Spanish, etc. So whether or not there are any black-owned or endorsed men's rights websites is irrelevant. All men will benefit. I say for those who are into fighting for causes, there's nothing wrong with picking a good cause, and I see nothing wrong with wanting to make the legal system more fair and less prejudiced against men.
I'm not into movements and joining groups, but for those who are, I say men's rights is as good as any. I'd even say that men's rights is, in many ways, a better cause than most out there with a huge following.
To Danger:
Don't worry about people like Solomon. Even if he doesn't want to understand or care, your efforts (or someone else's) will help him directly or indirectly at some point. Maybe years down the road he or his son or grandson will avoid being treated unfairly or robbed of his wealth or kicked out of his home because enough Dangers out there informed other people and a law gets passed that will help men be treated more fairly in family courts. Let that be enough.