The phenomenon of mass shootings has been studied extensively in the US. We know a lot about individual shooters. We know a lot about what is known here on MN as toxic masculinity, and this trend and individual trait has been linked to a huge number of shooters. There is a superabundance of material to study, both in the case of individual gunmen (it is overwhelmingly men who turn to this sort of violence), in male dominated communities online, and in society at large and in various kinds of media. Generalisations absolutely can be made.
Multiple books and articles have been devoted to the intersection of hegemonic masculinity and white heterosexual male grievance culture and the context of the homosocial hierarchy. A specific kind of culture and society creates a specific kind of monster. Mass shootings tend to happen in conservative areas where there is a rigid social hierarchy, with white heterosexual males who exert their control over the environment and all within it on top, and everyone else in tiers beneath them.
Very briefly, when you are the beneficiary of a society which is set up to be unequal, the growing power and influence of inferior people you've been brought up and educated by
your society to believe should be under your control and available to you can cause you to respond with violence, which your society has told you is completely appropriate when faced with a perceived threat. When access to women is seen as the validation of all the notions you have about yourself, it's only right that women, both individuals and as a class, must be punished for their temerity in rejecting you. They have power over you even though they are mere women, the power to keep you languishing in the hell of the non-alpha male, the beta boy.
Guns and the availability of guns is not "the problem which nobody dares speak of" in the US. It's been debated for a long time and will continue to be debated. Mass shooters do not appear in a vacuum. It's the problem of male entitlement and male violence toward women which is the last taboo in the US, as in most other societies.
Hence the tide of rape, of violent porn, of ordinary, common-or-garden domestic violence against women, revenge porn, and millions of daily micro-aggressions. Hence the appeal of conservative political agendas wrt women's reproductive rights, and the mushrooming of paramilitary groups spouting replacement theory and opposed to all social progress by women and minorities, blaming Democrats for everything they feel is wrong in their lives, and bearing a grudge against both individual women and women as a whole for telling them that their place is not at the top of the heap. Hence the online hate communities such as incels, 4 chan, etc, encouraging feelings of entitlement, objectification of women, and misogyny. Hence the preposterous letter of the father of the Stanford rapist pleading that a rape conviction would ruin his son's bright future, essentially saying, 'Don't you sub-humans know who he is?'
Hence also the fetishisation of guns as symbols of virility, with gun violence its ultimate expression and also the ultimate way to make challenging voices shut up. Gun ownership and the use of guns give meaning to masculine gender identity, and assert power. Gun use gives the otherwise very inadequate owner the last word. Hence the mass shootings.
Mass shooters have absorbed the fundamental tenet of the zeitgeist, namely,
that white heterosexual men should rule society and are entitled to use violence against social inferiors, be they racial minorities or women or gay men who challenge their status - and coupled with a strong sense of injustice on an individual and societal level, of rights stripped and status stolen, and guns easily available, the stage is set.