>Not only cannabis isn't a good painkiller, but it comes with very strong side-effects: it makes you totally unable to do any activity. This is fine for a recreational usage, but for a therapeutic usage, it's a serious problem. Especially when alternatives exist.
I disagree. There are varying levels of pain. The pain from being cut open and (metaphorically speaking) my spine scraped out with gardening tools, then being stitched up again is much more significant than pain from muscle aches, mild nerve pain and many other sources.
Cannabis was insufficient (for me) immediately (and for a couple days) after surgery. However, it was absolutely sufficient after three or four days.
Yes, the psychotropic effects can be debilitating, but that's not true for everyone.
N.B.: The observations below are anecdata, so obviously YMMV.
I find (as an InfoSec/Infrastructure guy) that I can't give the level of focus required to do my job effectively if I use cannabis regularly.
However, I know several lawyers and other folks with mentally rigorous professions that use cannabis multiple times daily and are able to function reasonably well. Note (as I mention above) that I am not one of those people.
The impact of cannabis on an individual is subjective and nuanced, so I don't accept your assertion that "[cannabis] makes you totally unable to do any activity."
In fact, different strains of cannabis (presumably based on THC/CBD/other cannabinoids levels) have different effects on different people.
I don't doubt your (and/or others you know) experience has been that cannabis is disabling. But that's not true for everyone in every circumstance.
Which is why I strongly believe (as I stated in the comment to which you replied) that cannabis and the chemicals it contains should be thoroughly researched to determine its impacts, both positive and negative.
tl;dr: I disagree with your statement because it was categorical, not that it was necessarily wrong in all cases.