Try mentally tabooing the word "medical" and review your positions on medical marijuana. My impression here is that you have strong cached thoughts about what does and does not qualify as "medical", and the difference between medical and non-medical reasons isn't as large as you think.
For one hypothetical example, if there was a drug that made average people into geniuses, would its use qualify as "medical", or "performance enhancing"? What about a drug that made below-average people average? What's the difference, except expectations about what constitutes normality?
"Medical" here means "matching what the average person would think of when told it is medical". That is, the word is intended to communicate, and what it communicates is misleading to a large portion of the intended audience.
Over at Scott Adams' Blog you can find a very fine example of using the 'Rationality Engine' to solve the social problem of assisted dying.