The New Left / Marxist to neocon or hard right pipeline is a thing. A bunch of the Bush-era neocons were former Marxists. There's a few notable present-day neoreactionaries and other hard-right types that were former Marxists.
Backing up a bit, I've long observed that a decent number of highly educated and intelligent folks tend to gravitate toward authoritarian politics. That's because, being smart and educated, they obviously know how everything should work and can centrally plan society with their superior intellect. Obviously.
Marxism/Leninism delivers that. So does hard-right nationalism and neoreactionary ideology. It's not a big jump. Basically it's a jump you make when you're either tired of losing (Marxism is not popular in the West) or you abandon nominal egalitarianism.
I said nominal egalitarianism because all authoritarian systems and political ideologies are inherently elitist. All authoritarian ideologies disregard the opinions of "lesser" people, who either don't matter (right-wing) or aren't smart enough to know what's good for them (left-wing).
I think this is the real basis of the "horseshoe theory." The horseshoe meets at the extremes because the extremes of the left/right axis are authoritarian and they have that in common. If you end up at one of those poles you've already decided you know better than most people and this gives a kind of "divine right" to boss them around. For the left it's "smart man's burden" and for the right it's "divine right of kings" type stuff.