They don't consider actual anarchists to be leftists if they get to know them. I got called a red fash and a tankie and even a Caleb Maupin on reddit even when i was still a committed AnCom, simply because these confused children couldn't handle opinions like "it's ok and often even necessary to use violence against fascists if you don't want marginalized people to get murdered" or "Amerika killing two million people in Vietnam was kinda genocidal, actually." You may note these aren't even particularly radical positions, there's completely middle of the road socdems who wholeheartedly and openly share these sentiments (at least in places were socdems can be considered middle of the road), but many redditors, even those who like to claim the far left label for themselves, are so insanely drenched in right wing bs that they cannot wrap their head around anybody being to the left of Bernie. Their entire mental process just derails when they're confronted with any position outside the nazi hellscape that is US politics.