[Question_Assumptions]

That's why it's called politically correct. The term, originally coined by university leftists to talk about something being correct through a subjective political filter. So of course whether or not something is politically correct or politically incorrect will depend on the political filter applied.

[Laissez-faire capitalist]

Within a relativistic context though, how can liberals know (with any degree of certainty) that any political filter should be applied, or that they have applied the correct political filter?

Again, they would have to relativize even their own subjective political filter.