I think the main problem is not so much that people don't condemn a specific act (which I believe most times is done out of the best intentions, but can also Islamic principles of Taqiyya & Kitman) but its that they cannot prescribe responsibility to their religion and nor should anyone else. That is too taboo, and there is your problem.
Would those people dare hold up signs criticizing Islam itself? No f-cking way! A JW can say they condemn child abuse, but at the same time absolve their "tribe" from accountability in it, claiming any who criticize watchtower are evil.
Are they there to show support for the victims? or to try and separate themselves from the evil?