To be sober means to be bodily free of alcohol. It does not mean to be free of drugs. For that we have the terms ‘drug-free’, ‘clean’, etc., and these terms can rightly include being alcohol-free, or sober.
It does not mean happy, psychologically healthy, well-balanced, or even organised. It could mean restrained or temperate, but, in an environment where the subject is an alcoholic, this meaning can be invoked only secondarily and not without ambiguity. Since we have adequate synonyms, as indicated above, we should deploy those.
But why should we not use the term ‘sober’ to denote desirable states of mind or types of behaviour, and use the term ‘not sober’ to describe their opposite? Because no two people will agree on what states of mind or types of behaviour ought to be thus described. In effect, the word ‘sober’ is used to describe states of mind that are agreeable to the speaker and types of behaviour of which the speaker approves. In either case, sobriety is in the eye of the beholder, and such usage conveys only the judgement of the speaker, failing to tell us anything at all about the subject.
By the same token, such usage introduces a perpetual ambiguity into any usage of the term, such that one is forced to use paraphrase (‘free of alcohol’, ‘physically sober’) to convey the true notion of sobriety.
What is worse, physical sobriety is treated as a trivial, entry-level objective, clearing the way for the real goal, which apparently is something called emotional sobriety. This is backwards. If my alcoholic friends were drunk but emotionally sober, I would be mortified: they might actually die of their alcoholism, with the fact of their emotional sobriety of little consolation to those left behind. By contrast, if my alcoholic friends were physically sober but ‘emotionally drunk’, that is a state of affairs which, although regrettable for all, can at least be promptly remedied, not least by virtue of the individual’s physical sobriety.
In sum, let’s use the term ‘sober’ in its proper sense and use the many other terms available in English if we wish to communicate our qualitative assessment of our own or another’s psychological health or moral probity.