I'm not expecting a response from you given your feelings about discussing this issue, yet I did feel a response to you was needed (and I also have at the moment the time and compunction to make an effort in this regard.) As well, I've noticed that you've made an honest effort to express your thoughts in previous gun related threads so I thought I'd "give it a shot."
Right up 'til the moment before those shots were fired at the field, the shooter was an integral part of the law-abiding folks you're referring to. After the shots were fired, he was suddenly separated from the responsible folks he was and was with like he had the plague, yet he is still identified as a person who has legal possession of a firearm (assumed) just like all those other "responsible folks" who own firearms, myself being one of them. IOW, there is no separating him from every other gun owner just because he all of a sudden became "the guy with the plague".
Pragmatically speaking, all we really need is a more efficient way to winnow out those folks that can't be trusted to bear those arms they now have in their possession or would like to own. If it takes the same effort as it takes to own a vehicle and run it on the public thoroughfares with yearly registration, notification of sale/transfer of ownership and re-licensing as needed along with a robust enforcement apparatus to "make it all real" and of which I feel is sorely absent at this time I'd be all for it. Holding a person accountable for their ownership of firearms is, IMHO, not violating their rights to own them. In a sense, if a person does not want to be a responsible owner, then they must be compelled to do so or face consequences commensurate with the risks they pose to the public at large.
However, it seems that a very influential sector of the gun owner crowd and the NRA do not want ANY kind of sensible regulations that aren't on the books no matter how full of fatal gaps there are and no matter how many more lives are lost from these existing gaps and lax enforcement/regulations.
There is common ground to be had.