An Irish Catholic I knew responded to a claim Wiccans used to make (Fortunately, most modern Wiccans don't make this claim) about their religion being the exact one practiced by the ancient Celts with "Then, shouldn't you be burning people alive in wicker baskets?"
Similarly, I've mentioned to Fundamentalist Christians, when they insist that all the Old Testament laws still apply, and that all Christians must keep practicing them (mainly, they're talking about things like homosexuality), that that means they can't trim their beards and should be bringing animals to Church for Sacrifice.