From what I can tell, this tankie stuff is bullshit. In the years I've been here, I've seen close to zero 'tankie' content from any of these supposedly tankie instances. There's like maybe one or two people on those instances who might fit the description if you search for them. Meanwhile, literally every day there are posts spitting on these supposed tankie instances. (And actually, it's again a very small number of people complaining - but they put their crap into cute memes to get traction).
I don't like the idea of shouting slurs at entire instances. In my view, if you hate those instances so much - just block them. Problem solved. No need to spew hate all over lemmy.