Yeah, I mean, most people in monster movies don't assume there are monsters around until they get some evidence; and handful_ofdust has praised horror flicks where the protagonist simply can't afford to listen to their gut and move out of the spooky house/quit the creepy job.

It's more the "hey, there's a known killer on the loose so let's all split up" characters whole make one's eyes roll.

Them! has one of the protagonists, a cop, blaming himself for leaving his partner alone at the crime scene while he gets reinforcements, only to have his boss point out (a) one of you *had* to stay, it's police procedure, and (b) the guy who stayed was a crack shot, and the other victims were armed and experienced too -- whatever we're dealing with seems to be bullet-proof and have more than human strength.