For me, it's a kneejerk attempt to categorize and thus dismiss, ideas I think worth examining thoughtfully, and I see kneejerkers on the far sides of both camps.
The loudness with which the kneeo's monopolize what would otherwise have been thoughtful discourse, keeps most center right and center left from being able to cooperate to get good things done.
I've been watching politics for over forty years, and the middle used to be able to ignore the far out wings. There's been a capturing of the primary process lately that works to the advantage of organized far right and far left activists, and leaves the disorganized center with little voice. I don't think the country is nearly as polarized as the media and activists want us to believe.