What would you think of a house rule where when you roll a 1, you get the option to re-roll, and if you fail on that you get a critical fumble? If you don't want to fumble, just don't take the re-roll.
I can't understand it, but some people feel they are worse off when they are given an extra option to take a risk.
Personally, I like the image of the desperate mage, overextending trying to cast a spell he normally can't control, with great risk to himself. Haven't really seen it well implemented, but I think that would be an interesting mechanic. Like, you normally can cast polymorph, and have fun with that, but in a perilous situation you may try to cast super-polymorph with some risk.