I didn't say don't understand them, I'm saying they're literally not thinking that deeply about it. They want to get a rise out of you and someone showed them they can do that by opening with a straw-man like this. By deliberately misrepresenting what "Tankie" means they can completely disarm it and force you to defend a position they chose, which they know is indefensible. It's pure rhetorical strategy, they don't actually know or care what a Tankie thinks. They're trying to make the word mean something it never has and never should mean. Is it possible someone on their side has done some work to rationalize their twisted interpretation. That rationalization is usually paper thin and almost no one on their side knows or cares about it besides its usefulness as a tactical fallback. They don't believe any of this, its a rhetorical game and the point is their nihilistic disregard for consequences.