SSC famously made and extended this argument a few years ago [0]. I like that essay's example of creationists even better, because it's a shockingly huge group of people - over 40% of Americans literally believe that the Earth was created in its present form in the last 10,000 years or so - and for all intents and purposes its overlap with the readership of PG, HN, SSC, or whatever is 0.
[0] https://slatestarcodex.com/2014/09/30/i-can-tolerate-anythin...
Coming from where I live, it's surprising to think of any of those (pro-life, pro-gun, or Trump voter) being quiet about it, so my feeling is that they are nonexistent in your circles, not quiet. But perhaps they are indeed closeted there.
FWIW, I also thought that SV (though not SF) was full of firearm enthusiasts and prepper types, but that's probably an uninformed view from the other side of the country.
I'm in one of those categories and I have managed to sniff out a few other people, but it's all very hush-hush. I'm the only one who is "out of the closet" in any way, and that's just because I didn't realize that people in blue areas found guns so repulsive.
Many people with beliefs that are widespread in the US (pro-life, pro-gun, Republican, etc) are now "in the closet" in the Bay Area. Don't believe me? 10% of San Franciscans voted for Trump in 2016. Yet of all the people I've worked with in the past four years, not a single one of them has publicly admitted to doing so. 14 percent of Californians own guns, but again, nobody I've worked with is "out of the closet" as a gun owner. That is an amazing coincidence. Let's say I've worked closely with 50 people in the past 4 years (the actual number is higher). If each one has a 10% chance of voting for Trump, there is a 99.5% chance that I've worked directly with a Trump voter. It's a 99.95% chance that I've worked with a gun owner. Yet based on everything I hear at work, you'd never suspect that such people exist. They're like dark matter.
If that's what life is like at companies founded by people who are aggressively independent-minded, I shudder to think how bad it is at companies run by the aggressively conventional-minded.