And, to use a hot take here, I believe that the "left to right" political axis can be simplified using a "I believe I am better than X" statement, where X is a set of people(s), that grows ever wider the further right you go.
Therefore a person on the "far left" of the axis would complete the sentence as "I believe I am better than nobody" and thus it's not really plausible that they would need slurs to talk about others.
I realize that this sounds a little of the "no true Scotsman" fallacy, but people saying they are something, does not make them that something unless backed up by actions/beliefs. Using slurs is antithetic to being any kind of left, not just "far", so I suspect you might have met someone confused about things.