The idea as a whole is good. I agree with many others about the fact it will make many (potentially) suicidal people survive longer, or even on the path of a long way to recovery, knowing that they always have the option of opting out if they really choose it. Furthermore, it would cull the stigma and also more people would be willing to open up about their suicidal ideation if the threat of incarceration, punishment, and other consequences (medical bills, mark on record, loss of job and social life) aren't present.
As far as collateral damage, yes I believe that is it unfortunate and in no way am I condoning it, but I believe there is a deeper problem and it's societal values, norms, and attitudes towards suicide itself.
This video partially explains one aspect of why society is shitty itself. If society and it's people really want to see change in the long term and actually really "fix" things, then it has to examine it's flaws, change it's attitude and approach towards suicidal people, and at some point, they can no longer suppress the truth or continue to wallow in delusions and ignorance (in other words, pretending that suicide prevention is the answer and the current way we treat suicidal people is effective.).
I agree that murderers ≠ suicidal people and there is a big distinction between the two. Yes, I believe the GermanWings guy should not have taken an entire plane full of passengers into the mountain. The same thing with the nurse, he should just quietly taken the drugs he needed to free himself from this existence which would not only save taxpayers' a lot of money but this also means he would not be rotting in prison for life (don't get me wrong, he absolutely deserved life in prison for his crimes of killing many patients, especially those without their consent).
Tbh, if I was a nurse, I'd probably won't need to rely on firearms as my method of ctb'ing as I would have my method accessible almost all the time.