I don't think shooters are generally led down that path directly due to economic stress. The shooter in your homeland NZ for example wasn't a poor and disaffected person.
For one.... a dozen guns are expensive.
It's not that they have nothing, its that they are being led to believe what they do have is threatened, and threatened by 'others'. That focus can be on Islam or immigrants in general or Jews or any number of targets.
Essentially there is a narrative built up that these individuals identities are at risk and when you have that environment some small number of people will take violent action to protect themselves or their society or culture.
At least thats how they percieve it, as their viewpoint is twisted and wrong.
That's the white suppremacist type shooters of course. There are other kinds, school shooters, incels, islamic extremists and each has their own set of disturbing influences and motivations.
All in all though, I buy economic stress as a factor in any crime but I don't think its correct to attribute this kind of terrorism to it.
No, it's not fair to go and shoot a crowd of people you suspect to be selfish in lieu of stupidity because they're all too stupid to realize their selfishness or their stupidity.
All that's accomplished is a crowd of shot down people who don't know what your on about and left over martyrs.
The ones who could use a good shooting are too spread out, hidden and protected.
As for the instance here in the land of the big long fart-ripped ozone layer - that was idiocy. I think the guy was influentially younger during the 9/11 situation and grew up in contempt because of it.
He blamed all Arabs for the actions of a small percentage of them and that's just simply ill-informed even if popular Middle-Eastern religion tries to assert that they are all the collective spirit of Mohamed.