I am relaying what I have learned as an experienced layperson, but I think you must say that these drugs are "relatively safe". Putting chemicals with noticeable medical effects into your body is something that is rarely 'safe' in an absolute sense.

Many drugs can be used safely, but there are very few drugs that cannot be used dangerously. There are even medicines that cannot be used safely that are nonetheless used in situations where they offer better odds than the alternative.

All drugs are either excreted renally (by the kidney) or metabolized (and possibly excreted) by the liver. Both of these can cause damage to the organ involved if the cumulative load of chemicals that need processing exceeds safe limits; the former is especially serious. In some cases with the latter, there can be cascading consequences due to the toxic nature of the metabolic products (as is dramatically illustrated by the metabolization of methanol).

This is why recreational drug use poses a quandary for regulation. If one is placed in the position of being responsible for determining that a substance is "safe enough" for unregulated use, it is very hard to determine a standard for making that decision. Ethanol, for instance, is clearly not "safe enough" for unregulated use. It is toxic, addictive, socially destructive, and causes thousands of deaths a year. Articulating a standard whereby one should, on one's authority, permit that people should be able to get themselves killed using some chemical one has never heard of: this is a difficult task. A regulatory structure that leans too heavily on authority --- rather than precedent, tests of merit, and community consensus decisions, for instance --- is destined to produce extremely conservative results.

I think that what these people are doing is great, and it is possibly a huge boon to large areas of psychiatric, neurochemical, and psychological research. It is clear at this point that some traditionally 'recreational' psychotropic drugs can have therapeutic effects in some situations. This will allow researchers to develop concrete evidence about specific protocols.

However, I am not sure that this is a first case for stepwise liberalization of drug policies: these are drugs that are medically interesting because of their specific effects, rather than due to the misrecognition of their actual harm. In my opinion, North American society is still at a point where we are just beginning to discuss marijuana seriously in term of harm, and the meaning of noticeable psychedelic & sensual effects are being mooted. There is already a cultural framework available for understanding and accepting recreational drug use, but it needs a lot of poking, prodding, and testing before it will be adapted by society at large. In order for drug policy liberalization to occur, there would need to be significant structural changes in policy, regulatory bodies, societal doctrines of use, and the social systems that deal with the social consequences of drug use, self-medication for dysphoric personal experiences, and non-self-supporting individuals.

For the record, have used and did enjoy psilocybin: based purely on the subjective experience, would use again, but it would be medically unadvisable for me at this time.