I'm not going to play any blame games, and am not in the position to do so. I think its likely that these guys don't just completely flip out on a whim though. There were likely warning signs of some sort, at least I'd like to hope so. The message I take from this kind of stuff is to be the best you can to your family and friends. If they have trouble, don't give up. Help them through, especially family...Never leave your family hanging. I'm not sure that will always work, but its gotta help at least.
The Tragedy in Houston might have very well been avoided if we had more common sense gun laws. Any person that seeks to purchase a firearm should have to undergo a comprehensive background check. All gun sales should be subject to background checks. We should also increase penalties for illegally purchasing firearms.
Yes, something could have been done to avoid the Houston tragedy, and it starts with gun control. If the killer did not have access to guns, would anyone have been injured? Why do we let these people buy weapons? Once the US stands up to the NRA, tragedies like this will be avoided.
No, nothing could have been done differently to avoid the Houston tragedy, because there is no way to protect everyone from everything. There cannot be metal detectors at every mall, movie theater, or sporting event. Americans still want to live in freedom, and that means taking some risks. It is just tragic when people are victimized.
In the Houston case, the shooter apparently had a pretty extensive collection of Nazi propaganda as well as a collection of vintage military items. Not clear how many weapons, but obviously someone who thought about and acquired items of war and violence. Unless we remove all weapons, or come up with a better way to identify people who are isolated, struggling, mentally ill, or with violent tendencies, not much can be done to prevent these kinds of tragedies.