To me, the Oxford shooting is a cautionary tale of being too sensitive and getting in the habit of expecting everything to be a false alarm.
I have a hard time identifying which steps actually went wrong. Specifically, some of those red flags are only alarming in combination with others, but treating them like problems actually causes too many false alarms that the school has been implicitly trained to ignore. I'd include in this a teenager who is allowed to go shooting, talks about it, posts on social media about it. All of this is perfectly legal and not even unusual in some locations. The teenager having his own handgun is technically illegal depending on interpretation, but a parent buying a gun and keeping possession of it but designating it for the kids use is fine, and kids would refer to it as their gun. And here we see the payoff that the school has been forced to react to all these things over the years when it's as innocent as if the kid were engaged in any other pastime.
The parents were apparently negligent here. They knew at the time they were called into the office that the kid had access to the gun. That's information the school didn't have.
The school should have had it, though. I think when you find a kid drawing violent images, it isn't in itself a cause for discipline, but it is a reason to ask questions. And a few of those questions should have been "do you have a gun in the house?" "does your son have access to it?". Those might have been enough to motivate a search.
Even searching ammo online is one of those things against the rules for no good reason. The way zero tolerance policies are often implemented is that the picture of the gun is treated as if it's a danger. Someone could have been scared by that. The "safety issue" is not actually a safety issue, and everyone knows it but they have to pretend. But then once they've gone through the motions, they forget that a kid drawing pictures of killing people might also be an indicator of real violence, not just "I'm offended" violence.
No it isn’t. Quoting your own source “ Live vaccines contain a weakened or attenuated form of a virus or bacteria.”. That is not what is suggested here.
Intentional infection through controlled means with the contagious virus hasn’t been used since Smallpox (as opposed to pox parties). There is no accepted term. The meaning was immediately clear to me on first reading it. It appears to be a successful reintroduction if a word for an analogous purpose. It’s even unique enough to be googleable.
Words are used to convey meaning. No one who has read more than a sentence on this topic thinks that Robin and Zvi are proposing the use of dried scabs. Vaccination is a word in common use for all diseases despite originally referring specifically to inoculation by cowpox ('vacca' = 'cow'). And it has a highly relevant parallel twin that refers specifically to the inoculation by the live dangerous virus, variolation.
I just registered to offer some perhaps not readily available information which may be relevant to your evaluation.
I heard Dave Grossman speak in person when I was in the Marines around 2005. I remember his emphasis on getting enough sleep, and less than 30 minutes at a stretch not being worthwhile, but I mostly remember my impression of a fanatic. By this I mean he did not come across as a rational person committed to introspection and careful evaluation of his own beliefs. The general opinion of a bunch of Marine combat veterans was that he was way too wound up and seemed on the verge of a nervous breakdown.
He started his talk with a story about how he won't take his granddaughter for a walk in the woods without his German Shepherd, a folding knife, and a concealed handgun. I can't say he's wrong, but I can say that whatever motivates Dave Grossman seems to lead to a view of the world that is very distant from what I think are rational behaviors.