If the old testament is completely irrelevant to Christians, Teribus, why is it included in the Bible that Christians use?

And what about Jews? Are you saying that we should fight everyone whose holy text says that all people who believe differently than they do should be killed? If that's that case, I guess you advocate doing to Jews what you are saying we should do to Muslims, because for Jews, it's all old testament.

Or do you just think we should kill Muslims and leave everyone else whose holy text advocates killing non-believers alone?