Not so slow. If you’ve ever experienced nitrogen narcosis (say from scuba diving too deep), you’ll know that the feeling of euphoria pretty much makes you unaware of anything, and the quick change to .05% O2 will render you almost immediately unconscious.
You’ve always had the ability to end your own life at method and time of your choosing. It’s called a big caliber handgun put into your mouth at an angle.
The right to life includes the right to take your own life if you choose.
I do not endorse doing so except under limited circumstances, but ultimately an individual has the right to make that decision.
For people with terminal illnesses, particularly in cases involving the likelihood of a great deal of pain, such as cancer, or likely loss of faculties, such as Alzheimer’s, I have zero issue with people taking their own life to avoid the pain or to avoid becoming a burden on their loved ones.
In other circumstances, I would advocate against suicide, but again, that is ultimately the individual’s choice.
So what’s next? Typically, they lower the standards to be killed. Then eventually if you are deemed to be a burden to the state, some cases will become mandatory.