True :/

My first thoughts on how it could be mitigated:

• If you're referred to the site by someone you trust.
• Signaling of quality. Ex. mentions of decision theory may signal quality to technically minded people. But there are other things that signal quality to "normal people". I'd have to think harder about it to come up with good examples.
• Design and activity. I'm into startups, and after failing at my first one, I've realized how important these things are. Design is important in and of itself (as far as user experience goes), but it's also important because it signals quality. People often won't give things with poor design a chance, because they notice a correlation between design and quality. A similar point could be made about activity. Seeing lots of articles and comments serves as social proof of quality.
• Proving quality. The "chicken-egg" problem of trustworthiness is encountered everywhere. But quality does seem to win (sort of). I sense that enough people do give stuff a shot such that quality does win out to some extent. If my thinking is on track here, then I think it'd follow that quick wins are important. It's important to have some "start here" articles that new readers could read and think, "Woah, this is really cool and useful! This definitely isn't one of those sketchy self-help websites. I'm not sure what the concentration of quality is on this site, but after reading these first two articles I think it's worth reading a few more to find out".

Honestly, my impression is that the obstacles of Lost Purposes and not wanting to identify as a rationalist are notably bigger than the obstacle of credibility.