Separate post for what I think about the subject, since I wanted to focus on the article itself in the first one.
To a fair degree, I do agree with Ryan that mental health is a significant issue in mass shootings. I haven't seen any convincing evidence that individuals committing mass shootings are mentally sound, and to be honest to assume they are - especially as many of them kill themselves at the end - seems presumptuous. And while it is not the whole problem, I would like to see some hard statistics on it before saying it's not a significant part of the problem. At the very least, there are problems in a society where multiple people every year come to the conclusion that they should shoot innocent civilians.
And as Lexicus mentioned, mental health is an established component of the growing suicide problem, so even if you look at gun deaths in general, noting that mass shootings are still a small fraction of that, mental illness is a significant factor there.
As for legislation, there is definitely room for improvement. Even the most pro-NRA people I know support at least some degree of background checks. A waiting period before acquiring a gun also makes sense, and has been
shown to reduce homicides. I can also see the logic for a limit on how many guns/how much ammo you can buy at once, similar to how there are restrictions on how much of certain behind-the-counter drugs you can buy at once, e.g. pseudoephedrine.
Examples: If you just started receiving treatment for depression, and you go to a gun store and want to buy a pistol, that should be a red flag. If you are on an FBI watch list because you've been posting extremist videos advocating violence against civilians online, and you go to buy several rifles, that should also be a red flag. If you've been buying two rifles and 500 rounds of ammo a day for a week, either you should be a certified distributor or owner of a gun range, or that should be a red flag.
I do, however, support the intent of the 2nd Amendment, and don't support drastic restrictions on gun ownership, at least to people who have not shown themselves to be a risk to themselves or others. I think there's a middle ground between restrictions for law-abiding, ordinary citizens, and the current state where essentially anyone can acquire a gun instantly, even if there's very concerning evidence over their intentions.
And mental health is part of the equation. If there are fewer people considering suicide in the first place, and fewer people tempted by extremist ideology, that in turn means there will be fewer people inclined to commit violence with guns in the first place. It will never be perfect, but especially with today's mental health system that can't keep up with demand, to say that increasing mental health care will not decrease gun deaths seems equally as nonsensical to me as saying there is nothing that can be done to help legislatively.