This would seem to be a case warranting not merely the serious attentions of the authorities, but a stiff sentence upon conviction. Nevertheless, the inclusion of the charge of "attempting to use a weapon of mass destruction" is indicative of a borderline-preposterous prosecution-creep, in which terminology and statutes ostensibly enacted to provide legal instruments for the "war on terror" are applied ever further down the chain of criminal conduct. This is the inevitable consequence of the federalization of much criminal law, and law enforcement work, but also of the (criminally) imprecise statutes enacted pursuant to the necessity of fighting an ill-defined war on a military tactic, not to mention the amorphous concept of a "new normal", a euphemism for increasing deference to executive/prosecutorial authority, the boundaries of which are less and less precisely delimited.
The nihilism of much of our popular culture, in which representations of violence are celebrated all the more when they are nonteleological (as in the "just because" of extreme horror/gore films), and in which some damaged young men strive for the celebrity of infamy, in emulation of other nihilistic killers, is surely a factor. Added to this should be another aspect of our popular culture, that often-feral and vicious tribalism of youth, with its pointless totemization of meaningless differences, along with the customary indifference of authorities in the schools. It's a part of growing up, you see. Take one sensitive youth, add popular culture, stir in a ration of teenaged angst, and mix in a few cups of social ostracism, and the phenomenon, in general, has its explanation. Which is to say the specific cases may well remain mysterious. Anyone desirous of practicing distance psychoanalysis is welcome to attempt it.
Nonetheless, no one should be surprised when legal mechanisms intended for the "war on terror" migrate downward; indeed, they already have in the "war on (some) drugs", though it is not at all obvious that this is everywhere a 'terrorist' phenomenon. Considering the panoply of legal measures enacted, and powers asserted, in the course of the 'war', this is an unhappy medium-term prospect for the Republic. Troubled youths who plot attacks on schools won't be the only malefactors cudgeled with these blunt legal instruments. That's not the nature of power.