Not much braver than shooting a bunch of adults if you're doing in to a gun free zone where people aren't allowed to defend themselves anyway. but did you intentionally miss the point? It's not the act of shootings defenceless people that's brave, but putting yourself at odds with the entirety of the rest of society is not something cowardly.
Jordan Peterson is of the opinion that many mass shooters fundamentally have a problem with human existence and wish to erase it, he generally refers to it as "the spirit of Cain". He references Tolstoy who thought that the bad of human existence outweighed the good, and anyone who didn't act on this realisation by killing himself was a coward. So, seems a lot of these mass murderers are acting on their personal convictions rather than just just surrendering to "mental problems". I think that's why they generally target innocent people, rather than going after Kim Jong Un or another worthwhile target if they were intent on offing themselves.