1 Monty: Why would Erwin and Ginny resurrect Hitler? They helped us defeat him.
2 Prof. Jones: Granted, it's a worst case scenario.
2 Monty: It's a most ridiculous scenario, is what it is.
3 Minnesota Jones: I can think of something worse.
3 Monty: And what's that?
4 Minnesota Jones: They could resurrect Bach and he could write more of those blasted Variations.

Doc Brown: Great Scott! Jennifer could conceivably encounter her future self! The consequences of that could be disastrous!
Marty: Doc, what do you mean?
Doc Brown: I foresee two possibilities. 1: coming face to face with herself 30 years older would put her into shock and she'd simply pass out. Or 2: the encounter could create a time paradox, the result of which could cause a chain reaction that would unravel the very fabric of the spacetime continuum and destroy the entire universe! Granted, that's a worst-case scenario. The destruction might in fact be very localised, limited to merely our own galaxy.
Marty: Well, that's a relief.