Sling Blade/Fridge

Fridge Brilliance

Much of Doyle's actions were to drive Karl out of the house. When he was playing with his band, he was trying to play as loud as possible to make Karl leave out of annoyance. When that didn't work and it became clear that the Band got along with Karl better, he snapped and threw them out trying to toss Vaughn and Karl out in the frenzy. All it took was him deciding to move in for good and put his foot down to make Karl leave after a brief confrontation. Or so he thought, since Karl killed him in the end.

When Karl kills Doyle, the family does live the rest of their lives in peace without the latter. However what happens after? Odds are they wouldn't visit Karl in the hospital. Even if they are grateful they may be somewhat terrified now that he's killed again. Or at best berate him for wasting his second chance. Even if he gets out he's probably gonna be harassed by the cops since Doyle is their friend.