In a just society, a Nembutal prescription would be available to any adult who asked for it and could articulate a clear wish to die, along with a non-delusional reason for wanting to die.
There is no compelling moral reason to force people to stay alive who do not wish to live. A few serious ethical justifications have been offered for the assisted suicide prohibition for the terminally ill, but it is doubtful that these complex ethical arguments, or the paternalistic arguments offered on behalf of people with disabilities, are what's really behind the general suicide prohibition in its political form. The suicide prohibition exists because policy has almost no thought for ethics, except for the poorly-realized "folk ethic" that is as far into ethical thought as most human beings ever get. "Folk ethics" allows people to tolerate things like slavery, female subjugation, and marriage prohibition for gay people. Real ethics does not.
A religious justification is not an ethical justification. In a democracy, a religious justification has about as much genuine ethical power as an appeal to aesthetic preferences. Religious people who wish to make policy arguments must still do meta-ethics. In our society, they rarely bother to do so.
People feel bad when they hear about suicide. Since suicide is sad, people wish to prevent it for sentimental reasons. They fail to consider things like autonomy and the suffering of people who are forced to stay alive against their will. These concepts are not as easy for a primate brain to grasp as the folk-ethical appeal of the suicide prohibition. The suicide prohibition existed long before our modern model enshrined mental illness as the sole possible cause of suicide; like the practice of circumcision, the suicide prohibition is a practice in search of a reason.
But there is no reason.
In regard to the suffering and humiliation of those forced to stay alive against their will, here's an Australian news video about an elderly Australian man with incurable mesothelioma flying to Mexico with his wife to illegally take home the veterinary drug Nembutal for the purpose of suicide. The wife wonders angrily why he can't just buy it in Australia.
Despite the humiliation and exertion of this effort, they are the lucky ones. Apparently, according to some reports, even this method is now closed to those who wish to die.