Deploy the Reductio ad Hitleram
NO. 4.
When confronted with an animal rights fanatic, say, "Hey! You mean you're like Hermann Goering. Do you know that in 1933 he said that anyone found guilty of animal cruelty or experimentation would be sent to a concentration camp? They really cared about animals, those Nazis!"

Psalms 118:8 It is better to trust in the LORD than to put confidence in man.
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Scarlet Chord Ministries   Isa 1:18