The same can be said regarding various religions. While there is room to disagree over the scope of certain commands, or whether certain statements are figurative, or how exactly to reconcile difficult statements [1], there are certain well-attested fundamental principles within most religions which are agreed upon by diverse sects. It is not a fallacy to point out that someone claiming religion X violates its core tenets and therefore is not legitimately practicing that religion.
[0] what makes NTS a fallacy is that irrelevant criteria are being used to exclude an entity from a group they actually belong to. It is not NTS to point out that James Doohan was a Canadian of English/Irish descent, and not actually a Scotsman.
[1] in texts I've read from many religions, oft-criticized statements would be better described as "difficult to reconcile" than actually inconsistent or contradictory. The example you give is not even particularly difficult to make sense of; in the Bible, everyone deserves death, yet Yahweh shows love and offers forgiveness to all, so asking His followers to do the same is not at all surprising.