As an American, I'm still often baffled by American Exceptionalism. Often people who say stuff like this have zero actual clue about how things are done in other countries. And it's laughable to call out the right to bear arms when just being suspected of having a weapon is enough to justify an execution by the police.
I recall the time the Japanese imprisoned the CEO of Nissan on trumped up charges and he had to smuggle himself out of the country to escape. Of course the US has Gitmo, but in general the justice system is remarkably fair compared to other countries, since its much harder to get a guilty verdict, which is why so many criminal court cases end with plea deals instead.
Especially considering the fifth amendment was specifically intended to allow for a militia to defend against the government, not to enable students to carry an automatic rifle into school—but here we are
2nd amendment, 5th is the "right to remain silent" etc.
Still, the issue with school shootings is mostly that it targets the wrong people. After school programs, community support for troubled youth, options for local service or a job placement program for kids would all be solutions, but the youth only sees other kids at school as the problem. If the system is so screwed up that a kid feels the need to take up arms to fight against it, then they should, but school shootings are unnecessarily cruel and generally fail to lead to progressive changes; more often than not they become justification for increases in the very authoritarian measures that promote the violence in the first place.
-Freedom of expression (can't be arrested for social media posts, can't easily get sued into the ground for libel[0])
-Right to bear arms (technically legal for citizens to organize their own militant force, though often discouraged)
-Right to remain silent (it is always advised to never talk to the police under any circumstances).
[0]https://en.wikipedia.org/wiki/SPEECH_Act