It's all they have! How dare you take their only argument from them! /s
You are 100% right though. It's a ham fisted deflection technique. I will defend them from people outright calling them fascists. Because there is a difference. But they are both authoritarian and in the end do a lot of the same things. Which should be discouraged no matter their intentions.
The problem isn't with the meme conflating tankies with fascists in authoritarianism, it's with the usage of the word tankie to refer to anything left of liberalism, that's when this meme doesn't apply. Tankie in the original sense (i.e. Stalinist), sure.