>This is certainly a good way to find out how to manipulate human bodies with drugs, but it does seem to be at the (cynical) expense of the guinea pigs

From the athletes perspective the "drugs" aspect is totally incidental. There are plenty of sports where people and up pushing there bodies to extreme and dangerous limits without drugs. The athletes always have to end up finding a balance in risk, and the need to find this balance wouldn't be abandoned with the introduction of a "drugs OK" domain, as far as I can tell.