It's their choice, really, and nobody should curb free speech, but Facebook is ultimately a corporation, not a nation. And as a corporation it should have some civic duty. As it is, they already are willing to either sell or freely give away the information volunteered by their consumers to advertisers. What would be wrong with them taking a stand with gender violence? Not a thing.
I do not believe Facebook should take action against gender and domestic violence content. If content provided on the Internet, via social media, that is legal, it should be dealt with by law enforcement. Facebook should not be held responsible, nor should they be held responsible, to censor what people have chosen to post.