I am not informed enough to say if its good to allow heroin or not, but for now I belive you, because you know more then I do. But on party-drug side we should allow soft drugs (the catorisation should be looked over again thats maybe not perfectly right seperated but a startpoint) because 1. nobody died from using mariuana but many many died from alkohol, so if we allow alkohol we must allow weed else its totaly arbitary. Then there is the cancer argument that is also strong in my opinion. So thats the arguing in pro and contra (in this case only pro ^^) but we should also allow them just because the people are adult, they should know what they are doing, if thats not true we did something really wrong in education and as community or family, and even than, most people are responsible enough to know what they are doing, and just to protect a minority (even that we do not succed, in countrys where its legal to buy or use mariuana less people use it) its not ok to disrespekt the adultness of the mass.
For medical use, you should at least have to sign a few times some papers who informs you about the risks, because here in germany most people just take what the medic tells them, without question it. So you should at least know that its dangerous what you are doing, but if thats granted and a medic also thinks thats what you should take now, than it should be legal.