I lean pretty far left myself. But this kind of comment is why I think the left keeps losing.

The person you're engaging with is presenting rational arguments and logic in good faith, and instead of engaging and disagreeing and presenting your own counterarguments, you're just labeling them a racist.

This is not persuasive to anyone. In fact, it massively hurts your case, as readers assume you simply don't have any good reasons to support you. And I'd say it goes even further, and hurts "the left" as a whole, as people are conditioned to view that movement as in support of silencing conversation. Fewer than 20% of the population wants to live in a world where legitimate discussion might have you branded as a racist, homophobe, sexist, fascist, etc.

And not only that, it completely weakens the word. If you use the word "racist" to describe pretty much anyone who disagrees with you, then suddenly it applies to the vast majority of people, at which point it (by definition) no longer describes behavior that society finds unacceptable. Then it loses all power to cause anyone to actually reflect on themselves, or to take it seriously when the charge is levied against others.

I highly recommend reserving these words for the specific and rare times where they actually apply.