Slaughter of the Innocent

Darth Maul takes a running leap over this in the fourth season finale. While most would argue that Maul had already crossed it when he killed Qui-Gon, Qui-Gon is a Jedi, Maul is a Sith. Nothing personal there. What is personal, however, is murdering a bunch of innocent people, including children, just to lure Obi-Wan for the sole sake of revenge.

Example of:
Moral Event Horizon