HM... Are you defending (authoriatharian) policys of historical socialism a lot? Because i am in the the left side of the political spectrum too, and didn't have this experience on Lemmy. Maybe its because I frequent European. Communities more often, where there is not so much red scare as in America.
I have also beend called a communist, also in real life, but this wasn't meant as an insult but as a description. I argument in favor of a democracy without capitalism, maybe with councils (strange that there seems to be no English word for "rätesystem" which doesn't involve worker or soldiers, which is to exclusive IMO), so calling me a communist/socialist is understandable and (apart from some very rare instances) wasn't meant to discredit me.
I have never been called a tankie though, and have never (even online) seen someone get called a tankie who had undogmatic views. People will defend dictators like Stalin, then define everyone who doesn't agree with Stalin as "libtards" and then get upset when undogmatic socialist who get mislabled that way call them tankies.
Sure, as with every buzzword misuse cases will exist, but most peoples argument is that they use the term for "everyone on the left spectrum" so its is meaningless, but for them the left spectrum only includes tankies, and they just define everyone else as not left.