I think what's missing in your assessment is time. Yes, in the short term allowing X in country Y might make country Z feel like they can get away with X. But

I think what's missing in your assessment is time. Yes, in the short term allowing X in country Y might make country Z feel like they can get away with X. But I think people generally have short memory, and anything beyond a generation (or two?) doesn't quite work that way. To be clear, I'm not saying you're wrong or proposing an alternative theory. I just think there's lack of evidence that you're correct, and personally I'm deeply uncomfortable with any form of punishment that isn't well-supported by evidence.