When Batman Beyond: Return of the Joker (2000) was in production, the April 20th, 1999 Columbine Massacre caused the editors to tone down the violence, remove references to violence and alter the demise of the Joker (Mark Hamill).
In the unedited version, a brainwashed Tim Drake was given a flag spear device that shoots out flags so that he might shoot at Batman.
“Make daddy proud. Deliver the punch line.”
Drake accidentally shot at the Joker, with blood coming out of the Joker’s chest.
“That’s not funny. That’s not…”
Tim Drake’s laughter transformed into tears from this.
In the post-Columbine edit of the scene, the Joker gave Tim Drake a device that shoots out Joker gas and wants Drake to brainwash Batman.
“Make him one of us.”
Drake threw the device away and pushed the Joker towards a flooded room filled with wires as Drake pulled the switch. The Joker dies off-screen.
Even though many DC fans were angered by the changes, the uncut version of the film was later released on DVD by April 23rd, 2002, three years and three days after the massacre.
It is true that after moral panics, things can be changed for a good reason.