Edit: Here’s a link to what is most likely the real manifesto: https://www.kenklippenstein.com/p/luigis-manifesto
Ken Klippenstein is a very reliable journalist and this version of the manifesto contains the snippets that have been released by law enforcement. Also, considering the thing was hand-written, that very long version involving his mom is dubious. (And there’s not any good evidence that his mom is in anything besides decent/good health)
The universal motivator for any kind of social improvement should be just that. Suffering breeds violence, whether out of a desperate need to survive, spiteful desire to pay back the pain done to them or a helpless need to reach out somehow for lack of a healthier way to cope. It’s not the only reason for violence, but it’s one, and to reduce suffering also helps to reduce violence.
Regardless of empathy or morals, a selfish desire for safety alone should push you to support measures that decreases the odds of you getting caught up in something.