[cvz]

Yes, you are morally responsible for your own actions. But those actions don't happen in a vacuum. They happen in a world that you are able to observe and make predictions about, however imperfect those predictions are. If you don't know that you're enabling the shooter, sure. But if you do know and do it anyway, you are responsible for knowingly enabling the shooter.

This doesn't mean that the shooter doesn't have his own agency and his own responsibility for his actions. It just means that his responsibility for his actions doesn't diminish your responsibility for yours, even if your actions involve him.

It seems to be a common idea that we can just overlook the abuses committed by the other people we deal with, as things "I'm not responsible for", regardless of our actual ability to do something about them. I have no special insight, but I think it's a common idea because it lets us feel better about ourselves while we do nothing. But "feeling good about oneself" isn't a solid way to build or evaluate a moral framework.