People should be locked in jail for being drug addicts. Give it a few more years and you'll change your opinion on that too.
If everyone on the entire planet was addicted to meth and did it daily, but there was a single meth user who decided to twerk naked at the top of the metro stairwell and assault people, that one person should be imprisoned. Why you ask? Because every other person on the planet is (as you say) functional. Nobody cares if you decided to do drugs and then fall asleep at home while paying your bills (ie: functioning). People do care about naked twerking people at the top of metro stairwells who routinely assault passers-by.
The aforementioned "functioning, respected and powerful people" are able to conceal or internalize the cost of their problems and aren't usually a problem for the public at large.
With that in mind, the problem is really just being persistently a public danger/nuisance. The only relevance of addiction to this is that addicts are frequently unresponsive to incentives that would be sufficient for non-addicts.