The short answer, in a cash game, in the situation you describe, is definitely never fold.
That you would even contemplate a fold in that spot simply proves that the stakes (at that movement at least) are too high for you to play correctly.
In other words - poker is all about finding opportunities in which you have a mathematical advantage, then using your chips to leverage and exploit that advantage.
If you're afraid to do that - risk your chips when you're a 75% favorite - you can't possibly be making correct decisions.
For what it's worth... if you're holding out for situations in which you're odds of winning are greater than 75%, then you're not going to have many chances to play.
For example - if you flop a set, and your opponent only has a flush or open-ended straight draw, you're still around a 75% favorite.
If you flop an Ace-high flush and your opponent has trips - you're only a 65% favorite.
Essentially you're saying that, unless you're sitting on the nuts, you'd fold to an all-in bet. That's clearly sub-optimal. Especially since your opponents will quickly sniff out your fear, and exploit it.
This isn't what you asked, but it's possible that you might fold AA in a tournament (under very specific circumstances.) But, even there - if you're knowingly folding the best hand, it's because you're willing to sacrifice any chance of winning in order to just finish in the money.
And, it sounds like you realize this, but if there are more than three people all-in pre-flop, it's possible that AA is less than 50% to win. (Although you're ALWAY the strong favorite).