Why misunderstand the point of "religion of peace"?

So some Muslims use violence, and then some joker walks in and says, "religion of peace, my azz" or whatever. Do they not get it? Muslims who commit violence or terrorism AREN'T LIVING UP TO THEIR OWN RELIGION. It happens in all religions. You know, like every Christian is a sinner. It doesn't mean Islam doesn't strive for peace, just that too many Muslims don't. A religion's teachings are just that - teachings. They aren't determined by how people actually act, otherwise, we wouldn't need teachings in the first place. The point of saying that Islam is a religion of peace is to shame terrorists into following their own religion for a change. If you think Islam doesn't teach peace, that's fine, but that's an entirely different issue.