That's not what I think motivated all the US school shootings in the last 25 years.
Ideological zeal that pursues actively harming others is something I don't think the US has much of, culturally speaking. No one preaches "those people need to die" or "we need to harm those people".
Still, as far as I can tell, even with the increase in frequency these are not common events. ~600 per year. No number of them is rare enough, but imagine if even 1 in 1000 of the estimated number of Americans who suffer from major depression (around 16 million) did a mass shooting. Running amok may be the exception that proves the rule.
I'd also point out that ideological zeal may play a role here. Ideology seems to underly policy of not only refusing to examine potential further restrictions on access but to broadly increasing access to arms/gear that make them easier. Characterizations of these events as mental health crises don't seem to lead to social policy supporting mental health. Certainly not the whole story, but probably plays a role in paving the way for harm.
https://en.wikipedia.org/wiki/%27No_Way_To_Prevent_This,%27_...
The UK had one mass shooting, twenty-five years ago, and chose to end the problem. https://en.wikipedia.org/wiki/Dunblane_massacre
Mass shootings are a horror that the US is unwilling and unable to confront. Far too many people would simply prefer to listen to Alex Jones and imagine that it's all fake.
Nobody says it out loud, they just strongly imply it.
Much like how nobody advocates for war by saying that <people in some other country should die>, they couch it behind nicer-sounding rhetoric.
.. yes they do? It's not usually spelled out in those words, at least not on the "respectable" side of the preaching, but when there's a mass shooter manifesto the shooter usually makes clear their influences and sometimes gives them thanks and citations.
It's also often done in the past tense. Whenever there's a controversial shooting, hundreds of commentators will turn up to say "that person deserved to be shot".