Is it possible to create a free speech reddit alternative that doesn't immediately turn into a right wing extremist site? My mind immediately turns to the Paradox of Tolerance, and I think the answer is no.
My guess would be that there's already a limit to their tolerance. And from there, it's really a matter of seeing what kind of content they _do_ tolerate.
A site full of extreme* right wing stuff: That site is an extreme right wing site. If it is indeed "free speech" (which isn't demonstrated yet), that's merely coincidental, but it's not its defining property.
* To adopt hunterb123's preferred phrasing, because for them extremism apparently only begins when people start to draft assassination plans, not just daydreaming about it. I don't care about that particular semantic game, so I'll be as compatible as possible on this thread.