If the rifle receiver fails structurally the case head is pretty much guaranteed to blow. This happens on low number receivers and I have at one well documented National Ordnance M1903A3 which set back and blew the case head. If the receiver seats are moved back, due to weak or soft metal, than the case head is moved out of the chamber. Shooters are pretty much unaware of the importance of cartridge case head protrusion, it is far more safety critical than the dimension from base to shoulder. Too much cartridge case head protrusion and the side walls blow, or if you want to call it, the case head blows.
Now of course there are "good" single heat treat receivers, but no one knows how to non destructively test the things, and the only real way to tell a good SHT from a bad SHT is whether the thing has blown up or not. The fact that some are still around is not proof that existing receivers are good, they may be only a few rounds away from fatigue failure.
I only have one life and an not interested in firing something I don't have full confidence in. Nor am I going to try to convince people that the risk is small, like Dr Lyons. Single heat treat fan boys base their arguments on ignorance. They have not heard of, they don't know, prove it is unsafe, etc. That standard is not appropriate anymore, at least for product liability. Now days, you have to prove it is safe. I would like single heat treat fan boys make a case by metallurgical analysis, failure analysis, structural analysis, test, why all single heat treat receivers are safe. If one is unsafe they will have lost their argument.