We shouldn’t fall into a trap of defining what’s extreme as a deviation from the mainstream liberal bias in the west. In my view the idea that a minority of people should own the means of production and dictate the economic reality for the working majority is what’s extreme. It is true, that Marxists advocate for extreme measures for overthrowing an extreme system though.
I generally agree, however whether something is reasonable or just has little to do with deviation from the norm. It’s linguistic gymnastics, really. Marxism is extreme in the sense that it is a firmly Leftist position in a world dominated by Capital, but is perfectly reasonable at the same time.
I dunno, more of a monologue than a response, but I hope it cleared up my intent.