I keep wanting to form some kind of housing cooperative for people seeking refuge from abusive situations, seeing as how there's currently fuck-all meaningful resources for adult survivors of childhood abuse. I know that despite this being completely nonviolent, legal, voluntary, and well-intentioned operation, that most people won't care or will actively support when some extremists decide to infiltrate and sabotage that effort. Manufactured consent and all. Why does nobody else do things like this? What has prevented the vast majority of other American leftists from simply crowdfunding their own communes, leaving the larger economy, and building their own means of production so that they aren't dependent on the rest of the world for permission to build systems of mutual aid?
There's a lot of different questions here. Let's take a crack at 'em.
Housing cooperatives, intentional communities, and communes are not quite the same thing as each other. Every commune is an IC and every IC has cooperative housing, but this doesn't go the other way around. Even Bernie is known for paving the way for land trusts in Burlington. Do you want a sort of affordable housing nonprofit, or do you want an income-sharing and wealth-sharing community, or something else?
"Why don't American leftists just crowdfund their own communes?"
Mostly because they don't realize or accept that it's a thing they can do. They have the motive, but lack the prompt and a recognition of their ability. In my experience it seems like you can duck your head around any corner and find people with a strong desire to escape capitalism. One of your questions (what do you do about people dogpiling on you as soon as they find out about you) kind of answers another of your questions (why do I not see this sort of thing everywhere). Lots of these things keep a low profile. It's kind of like a communist version of the Fermi Paradox. Just a few months ago I got in contact with a leftist land trust less than 200 miles from me. They maintained a lot of stipulations about not drawing publicity.
Probably the best way to find these places is by talking to other leftists IRL. Of course, they'll need to be the kind of leftist that actually does networking and connects with other leftists, not the kind that just sticks their thumb out and hopes for the Revolution to pick them up. The number one way to poke your head underground is to participate in struggles. If you have the ability to, I recommend you visit the Atlanta Forest occupation. I cannot guarantee any outcome but I promise you there are lots of good contacts there to be made.
I have a friend who's more of an expert on the matter of cohousing than I am. One thing he told me recently that I really held onto was "be wary of having a living arrangement where everyone is unpacking/dealing with the same kind of trauma". It was an argument for diversification, against concentration.
Building your own means of production is an interesting issue. The most I've heard of a single entity building up the MoP is the Twelve Tribes, and they're kinda culty, even if they do have very extensive vertical integration. Theoretically, if you were to build up an alternative economy within the borders of the USA, and the governmental apparatus correctly identified you as something limiting its power, it could use any and all of its tools (eminent domain, executive orders, phony charges, police action, National Guard) to eliminate you. But that assumes that the capitalist apparatus is coherent and unified and intelligent.
Perhaps what we have to do is analogous to what China did under Deng: plant ourselves deeply, make ourselves indispensible to the American economy such that any attempt to uproot us would be massively self-destructive. Homesteading is most certainly not a profit-maximizing endeavor, and millions of Americans are homesteaders; yet we don't see the government cracking down on homesteading to wring more profits out. I think collective homesteading, that maintains revolutionary integrity while keeping a low profile, is a good strategy.
My biggest personal piece of advice to contribute is to not try to be the only game in town. You need to be prepared for people and groups who are incompatible with each other, and to either orient yourself towards one and not the other, or to provide multiple spaces where they won't clash. Also if you have one space that is where a lot of radical activity is concentrated, you'll become a sort of boogeyman or "usual suspect". There is safety in spreading out a bit, and interspersing with people who are outside your group or peripheral to it.
That, along with a non-confrontational orientation, should be enough for the feds and most of the chuds to leave you alone. You may have to put some efforts into PR. But the bigger threat is actually internal factors. Reactionary forces in this country (and others) have relied a lot on the pressures of activism and late-stage capitalism to wear down activist circles. There will be people who have a bad experience with you, peel off, and become your haters; you can minimize this but you cannot avoid it entirely.
People who have lived "in community" echo that the perennial problems are about drinking, drugs, dogs, and dishes. Another issue is the dynamics of dating. Relational drama can tear apart organizations. This is more prominent in rural settings where your pool is severely limited, and less prominent in urban settings. The reason why people buy land in the country, though, is to not be constrained by zoning codes and busybody neighbors.
I would conclude that the external pressures are higher in the city, and the internal pressures are higher in the country.