What Is the Free, in Free Trade?

I'm wondering why are subsidies for industries and even tariffs seen as a contradiction of trading principles in the first place. I mean, after all, is our underlying norm essentially one of a perfectly homogenous condition, you know, almost like a chess game? You know, wage costs or natural conditions that favor one country rather than another? Those are legitimate reasons for comparative advantage in a pattern of trade, as opposed to interventions. It's an incredibly fragile set of distinctions which are implied by these conventional understandings. And if you accept this logic, then really, the distinction breaks down.