Follow it through
"If that's true, what else would have to be true?"
Recorded by Plato · Euthyphro 7a–8a
Take the claim seriously and push it one step further. If the result is absurd or clashes with something you know, the original claim has a problem.
Euthyphro says holy means 'dear to the gods', but he also holds that the gods quarrel. Socrates follows it through: 'And then the same things would be both holy and unholy, Euthyphro, according to this statement.' (8a)