Doing baron while you're behind isn't a bad idea, actually, it's actually kind of stupid when you're ahead. If you suceed at getting baron while behind, you might just win yourself the game (or at least buy a few more minutes to try and get back in the game), if you don't manage you lose, but if you don't do it at all you fail anyway.
It's the exact opposite when you're ahead though, if you get it, you win, if you don't do anything, you win, but if the enemy team ganks you at baron, that might just lose you the game.