The main problem with joining a cult isn't physical danger, or even the chance of having your mind permanently changed (retention rates for cult membership are very low). It's what they'll get out of you while you're in there. In most cases you can expect to see a lot of pressure to do things like handing over large sums of money, or donating large amounts of unpaid labor, or abandoning social links outside the organization, and those aren't necessarily things you can get back once you've burned them.

I'd expect going in with eyes open to mitigate this to some extent, but not perfectly.