Since “liberals” are inherently reactionary even the most “progressive” among them, like their conservative fellow travelers, believe in the idea of a “radical left.”
Communists and socialists are becoming less taboo as words so they use the euphemism of “tankie” to denote the left they deem radical.
The problem is those “radical” positions are like unwavering anti-racism so they can’t condemn that because the alternative is being “pro racism” (note, the chuds squared this circle by being “anti-antifa” the lib solution is a bit more overwrought) so instead they just condemn a nebulous “tankie” occupying the end of a political spectrum only they believe in.