I agree that if you're only complaining or defending people you agree with, you are probably engaging in inconsistency. But I think there are lines that can be drawn. They are tough to ferret out, and they will always be subject to disagreement, but that doesn't mean one is a hypocrite or inconsistent.
Re First Amendment issues, I'm an absolutist. The govt should not censor or fine you for any opinion expressed based on the merits (even this has a fuzzy line with incitement and I recognize that).
Re private citizens "cancelling" each other through social pressure, someone posted a tweet from a DC area lawyer and I think she got it right: normally, we should want to have free speech and debate with people who disagree with us. But some opinions are so far outside the norms of a civilized society, that debate isn't helpful and those people should be shunned (socially by those who care about that issue).
Defining exactly where that line is, is difficult, maybe impossible. But I don't think it's difficult to say that (1) defending the butchering and burning alive of babies and raping innocent young girls is one the wrong side of the line, and (2) aligning oneself with a Trump-era policy (wanting a border wall built, or fewer immigrants) is on the debate-side of the line. (I also think BudLite is on this side of the line).
You're right that a lot of gamesmanship can be played in moving these lines. But I think those worried about cancel culture before were complaining about where the line was being drawn, not that there might be a line at all.