I'm sorry about your gitlfriend's experience. I agree that these substances are quite powerful and should be handled with great care.
> I am unconvinced that throwing psychedelics at mentally unstable (unhealthy) people is a good idea.
Fortunately, this isn't what happens. The medicine is administered in sessions with experienced therapists present as guides. Extensive therapy sessions are also conducted in preparation for the treatment as well as for follow-up.
> I do believe that we should allow researchers greater flexibility to experiment with them because it would be worthwhile to understand more about why psychedelics do what they do.
This is (finally) happening. The results that are coming in are quite amazing. For example, the use of guided MDMA therapy sessions to treat severe PTSD was actually granted "breakthrough treatment" status by FDA. It is currently in the last phase of trials before the treatment is FDA approved.