Out of the ten worst mass shootings in the US, five were attributed to mental illness, that’s not including the Las Vegas shooting as a mental illness, which it may turn out to be. One was a terrorist attack. That leaves 3 or 4 caused by ‘domestic’ issues.
20% of all mass killings are committed by the 4% of the general population that have a major mental illness. That is not even to speak of those who have a minor, or even a transient, mental illness.
Massive problems plague the US regarding treatment of mental illness. Those problems are what need attention. Fixing those problems are what will give struggling people a means to satisfaction rather than having the rare outcome of a mass killing by someone who has been forgotten on the fringes of society, or someone who will not seek help for various other reasons, of which also need to be addressed.