Going back for a minute to foolish crewmembers, I should probably add a mention for Crewman Darnell from The Man Trap. While he didn't actually snack on a borgia plant as Nancy suggested, neither Kirk nor McCoy thought it too far fetched that he might have done. You'd think there would be some sort of Starfleet training about not sticking everything you find on an alien planet in your mouth, but apparently not!
Yeah, it's clear that the security teams need WAY more training than they got in the 60's. Er, I mean the 23rd Century.
Of course, since the TOS team was making up an entire world -- while working at a breakneck pace and doing everything as cheaply as possible -- what's surprising isn't that they got some things wrong, but how many things they got RIGHT.