Tactic

Taking the roof off

Grant the view for a moment and walk it to the cliff.

How

Adopt their principle for the sake of argument.
Apply it consistently to a case they will not accept.
The goal is to show they already believe more than their slogan.

Questions to keep in your pocket

If that rule were true in every case, what else would follow?
Would you still say that if you were the one being treated that way?

In the wild

‘A thing is okay as long as it doesn’t hurt anyone.’

Ask about a harm the victim never feels. If the act is still wrong, their rule is too small. Relativism lived out is not a free spirit; it is a person without a conscience.

This is a reductio, not a gotcha. Keep your tone as if you are thinking aloud together.