Are you married with children? You don't just go blowing holes in walls. A dog is a great deterrent. Ask any criminal and they'll tell you outright that it's difficult to negotiate with a dog. Dog, person at home, person at home that may be armed would the best deterrent to any burglar.
Did this guy show up on any mental radars? Sounds like another case where the mother had inside knowledge of issues with her son. A LOT of physiological changes occur in the brain in the late teens/early 20s.
Or let's play the hypothetical games. Women are known to have postpartum depression. Should all births, miscarriages, abortions be alerted to the government so that they could be put on a predetermined gun ban period to prevent them from going to get a gun? What about job loss, divorcees, widow(ers), kicked out of school, etc. Do we need to red flag all these potential depression catalysts on people to prevent them from purchasing a gun during a low point in their lives? If not, why not.
Although there's no evidence here this guy was deemed mentally unstable, even if he was how would the government/private enterprise deal with the privacy issues surrounding one's mental health and right to own a gun. You just can't make stuff up out of whole cloth without taking into consideration all liability and constitutional concerns. Otherwise it would just get blasted in the courts.