For one, the people on 8chan are absolutely a hated minority. That's largely why they're getting banned from the internet. Mainstream figures aren't coming out in favor of 8chan, they're calling for it's dissolution. Saying you visit or enjoy 8chan in polite company would likely be a faux pas if anyone even knew what you were talking about.
Of course, pretending to be a hated minority may be a rhetorical tactic - but that doesn't make it untrue. The Westborough Baptist Church may have experienced enhanced camaraderie from being almost universally reviled - but that doesn't mean they weren't, in fact, almost universally reviled.
"Authoritarian" also seems like a poor description. The boards are anti authoritarian in that they have lax moderation. There isn't a punishment for unwanted opinions - you can't be downvoted or shadowbanned. People can't even judge your future posts by the content of your previous posts because everyone is anonymous and without a post history. Banning is by ip only, and easily avoided, and there aren't even accounts to lose. 8chan is much more anarchic than authoritarian. I'm making that claim based on their structure rather than their political ideology.
The idea that Silicon Valley is not left wing also strikes me as highly suspect. For example, in the last Presidential election Clinton received 95% of Silicon Valley donations compared to 4% for Trump [1]. There are other, similar reports, for specific companies and different elections, but everything I've seen slowed they skew heavily left.
I'm aware that there are conceptions of "left wing" where Clinton wouldn't really count as left wing, but so long as we are discussing American politics I don't think those alternate conceptions are relevant. Clinton is clearly further left than Trump.
1 - https://fivethirtyeight.com/features/nearly-all-of-silicon-v...