I've been noticing the framing "imagine if the roles had been reversed... the reaction would be totally different!" more and more, especially around contentious

I've been noticing the framing "imagine if the roles had been reversed... the reaction would be totally different!" more and more, especially around contentious issues. I've never found it compelling. The argument seems like a variant of begging the question: we just saw that X caused Y reaction, but the argument asserts (generally without any evidence) that if the roles were reversed, then X' would cause a massively different Y'. Would it? Why? If we agree that it would, what does that demonstrate?