"Possession is nine-tenths of the law." That's the "legal socio-economic context". If it's worth having, and there's only one, so that if you have it nobody else does, then some people will want to have it with or without legal sanction.

And, a thing's economic value is derived from what someone else will pay for it, and only that. If someone else (or several someones) will buy it, whether or not the law agrees that it's legal, then the thing is valuable. (See drugs for an example.)

I wouldn't say that such people have a mental deficiency. A moral deficiency, yes, absolutely, but not a mental one.