Unfortunately, paranoid ideation can be linked to violent behavior, especially
if its linked to substance abuse. It doesn't always happen but it can. Was this guy using drugs or drinking? Who wants to risk it?
There is controversy whether associations between psychosis and violence are due to coexisting substance misuse and factors increasing risk in nonpsychotic persons. Recent studies in clinical samples have implicated independent effects of paranoid delusions. ...
www.ncbi.nlm.nih.gov
You also don't have to be psychotic to have harmful levels of paranoid ideation. The linked study was done in England, where guns aren't available to the general public.
Paranoid personality disorder (PPD) is a mental health condition marked by a pattern of distrust and suspicion of others without adequate reason to be suspicious.
my.clevelandclinic.org
JMO, buying guns, especially military grade automatic weapons, is not a good idea for people with this disorder, yet it happens a lot.