I like the idea that the turn to the Dark Side is not seen as a negative initially. Uncle Palpatine could be seen as the edgy radical as oppose to evil overlord, who achieves his goals by any means as oppose to doing the boring grown up thing.

The realisation that things have gone too far might be the point where we discover Obi-Wan isn't dead after his assassination or when Windu confronts Palpatine (You're in too far to turn back now boy!)

"Episode III - The Secret Apprentice" perhaps?