It used to be a word for people who defended Stalin sending tanks to Hungary in the 50s. It caught on in leftist discourse as a word for leftists who excuse illegitimate state violence, domestically and abroad

Correct etymology of the word!

Though on Lemmy, like reddit before it, it's mostly thrown around at anyone who disagrees that the US used to a be radiant light in the world until 2016 or anyone left of Pelosi

LMAO no much worse, it's "leftist I think is crazy", so who is and isn't a "tankie" depends on the person using the word; although it generally means someone who is pro hardcore Communism a la Stalin.