"How can you view the centrist neoliberal establishment as a "lesser evil" after all they've done? Obama was a literal war criminal! I'd rather side with [far-right nationalists/far-left socialists] against the status quo, we can worry about what the new system will look like when we've taken down the old one."
I think the main issue I have with these sorts of arguments is that they judge the establishment for what it's done while in power, but they only judge radical extremists for what they've done so far, despite the fact that those extremists aren't in power. But I would judge extremists not just by what they've done, but by what they say they'll do, and what they're likely to do if they ever do succeed at taking the reins of power for themselves.
Yes, the Obama administration started wars in the Middle East and carried out drone strikes without regard for civilian casualties, so you can argue that Obama is "worse" than Richard Spencer in some hardline utilitarian sense. But I think that's a deeply flawed way of looking at the world. If Richard Spencer and his allies were in power - if he was sitting in the Oval Office, and his fellow Neo-Nazis occupied the seats of Congress - they would make Bush, Obama, and Trump look like pacifists by comparison.
They would be butchers on a scale unseen in the Western world for nearly a century, carrying out brutal and horrific violence to a degree that would utterly dwarf Obama's crimes in severity and magnitude. And the same goes for their tankie and revolutionary leftist counterparts on the other side of the political spectrum.