I just don't see how two wrongs are better than one. "Women's right to choose" is constantly under attack from the right (and it certainly is), and it's something that they have never been able to rest in defending. If they didn't perceive men as constantly attacking them, they might be more sympathetic to men's rights causes. Women do have a recent history of real oppression, and they are sensitive to their hard won rights being reversed...
I hate social justice bullshit as much as the next guy, but I value individual rights. I don't see any benefit to attacking them in any way--it sets the precedent that individual rights are not worth defending. Why not defend women's and men's rights? Or at the least not actively attack women's rights? Men's rights are important, feel free to get out and march for them--that's what the women are doing because it's necessary to defend your rights or they will be taken away.
Sitting around arguing against abortion is quite an indirect way to achieve your goals with regard to bringing attention to men's rights and parental equality.