Different groups might well have different ideas of what an "informed" decision is.
I think at the very least when a player says they're making a decision that makes no sense to you, you have to make sure the player didn't forget something their character would know or isn't misunderstanding something about how the rules or game world work.
That requires talking out of character and basically asking "what is it you're trying to accomplish here" The most likely response is probably #1 - they forgot a vital clue, but it might be that they misunderstood something about the rules or basic situation. It's up to the GM to correct this because the GM is both the character's senses and the one who decides how the rules and game world works.