What are movies in which some of the dumbest reasons are provided by a killer for killing a said person?

Dr. Alphonse’s reasoning for killing the children in Forensic is one of the dumbest reasonings I’ve ever seen in a movie, yet.

Basically he is diagnosed with cancer, with little to no guarantee of whether he’ll live long or not, and it hurt him a lot, especially since he was a single parent and his son had no one else to dote upon.

And when he sees his son’s mates’ parents being happy with their kids, he gets psychologically triggered and goes on a killing spree, just because he saw some random bloke being happy with his kid.

It’s even worse when you realize that not only does his cancer get cured, but his son finds out about this and dies after falling off of their house’s roof.

And it doesn’t end there. Just to prove that the bus driver was not the killer, he kills another kid and goes dark.

Then he resurfaces a decade or two later and begins killing children again.

Like bro, wtf?