There is usually a very high bar for adjudicating someone mentally incompetent or for having psychologists at a mental hospital petition a court to have someone involuntarily hospitalized.
To simply assume that either would have occurred is absurd, and your counter to Vetplus necessarily requires one of the two.
You can't view these things in hindsight. Now we know he was a danger to others, but you can't judge things in hindsight if you're seeking to cast blame. The article you posted on page 1 gives a bare-bones overview of what must be found, but does not give you the set of standards that are applied or examples of cases where someone has been committed or found incompetent.
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And how do you know that if you aren't an expert in the relevant field?
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Again, how can you be so certain?
The article you posted simply lists the ultimate conclusion that must be reached for an adjudication of mental incompetence - "is a danger to himself or others or is unable to manage his own affairs - and does not even state the ultimate conclusion that must be reached for a court to grant a petition for involuntary commitment. You can't just take a phrase from an article and say "yup, I personally think his history would lead to this finding" if you want to have a meaningful debate about it.
It's like when someone takes the bare text of a constitutional amendment, then starts simply pronouncing what is and is not constitutional based on their personal feeling about what the text means. That's not how it works in law and its not now it works here. You can't just assume if you intend to make a valid point.
So...what exactly about his history makes you so certain that he'd be held one way or the other? How closely does his personal history match that of people who have been adjudicated incompetent or involuntarily committed? How much does it differ from those where the finding was not reached or the person not held? How can you know how he would present to the psychiatrists that would interview him?
The bottom line is that we don't know and if anyone is going to opine about the likelihood of him being held, thereby triggering FL gun laws, they should probably have significant experience in the field and be able to explain why X,Y,Z, about his history affected that likelihood.