Here's the problem: there's a difference between desperate and starving. You can go a long time without food if you were previously well-nourished - upto 3 weeks or so with no real problems. Which means you have a long time to realize you're in trouble, rally your allies etc.
People think that people turn on each other at the drop of dime - but they don't. The first thing desperate people do is forge alliances they might otherwise not consider, and then go looking for a solution to their common problem. They might eventually fall to infighting, but so goes the entirety of human civilization. We are fundamentally a tribal species, if we weren't then there wouldn't be a civilization to fall in the first place.
And it's not like this is a particularly difficult benefit to sell to people either: if someone's stockpiled enough food for a year, and there's 10 of you, then you have enough food for over a month if you knock over their hamlet. Heck, you can sell this idea to people who might be morally opposed, because you can leave them enough food for a month, and reasonably expect to knock over another hamlet before that time is up.
The economics and history support the only sensible conclusion: people who go it alone die out. The Mongol horde wasn't so much a horde as one of the most well-organized and powerful empires for its time, it only seemed like a horde because every village was happy to sell out its neighbors and hope they would be passed over. And the exact same problem applies to survivalists: they think the way they do, because they've misunderstood some very important things about the human condition. Worse, they think they're smarter then everyone else which means they're constantly underestimating potential allies and actual enemies.