Destroy a liberal's argument by exposing the underlying rhetorical cheat.
NO. 3.
The motive fallacy. This is a common technique used by liberals to dismiss facts that don't suit their argument. For example: "Well I'm not going to believe anything X says about this. X is funded by Exxon." Simply point out that just because somebody has a reason to believe something doesn't necessarily mean what he believes is not true. As philosopher Jamie Whyte puts it: "A man may stand to gain a great deal of peace and quiet from telling his wife that he loves her. But he really may love her nevertheless."

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