It is easy to marginalize this as bowing to political correctness. What brings it home for me is the actual classroom experience where you can visibly see a significant portion of the class tune out with the reaction "this is not for me" if you start to focus on shooting, exploding, killing etc.
With Scratch I can build lessons around music, art, and storytelling that teach the same programming fundamentals and are much more engaging to the girls who don't play FPS or RPG shoot-em-up games. Those inclined in that direction always find ways to introduce some explosions and blood into their projects, so it is not really at the expense of their experience.
I raised these concerns to the CodeCombat team on their forums several months ago when I first looked at their offering. They acknowledged that their platform could be used to design non-violent activities, and maybe they have done so by now. I could see how they could build some resource gathering or other missions that don't require killing.
Something that would get 75% of your students involved sounds like a huge win compared to standard curriculum programs, as soon as a class is required it's going to involve people that have 0 interest in it from start.
I do however agree that a required class does pose an engagement challenge. Computer Science will be a compulsory subject for UK school kids from September.
As for complaints, I think it's important to respect some parents' wishes for their kids not to play games that include killing. Although most parents wouldn't complain.