Insofar as that infighting takes the form of fighting over who is the most or trueist left, casting their opponents as not actually left, there is no contradict

Insofar as that infighting takes the form of fighting over who is the most or trueist left, casting their opponents as not actually left, there is no contradiction here. The eagerness to use shibboleths, slips of tongue and anecdotal correlations to identify impostures who are merely pretending to be left for underhanded rhetorical reasons is an example of this. Crypto-fascists are the ultimate boogieman. BTW it's not hard to find examples of the right doing this too.