Besides all of the stated reasons to legalize/decriminalize, I think just as important is personal liberty. I should be free to experiment with my own consciousness (so long as it does not impede on the rights of others) - how much more personal can you get? For the government to impede on this is unconscionable (pun intended).
> so long as it does not impede on the rights of others This is really the crux of the problem. How do you suggest that you legalize all drugs and then keep people on those drugs from harming others? Public safety has a hard enough time without having to deal with some unknown number of additional people that would try drugs are harm themselves or others if those drugs were legal.
It depends on what you mean by that.
If you mean they harm others by going on a drug fueled rampage, there isn't much we can do but react when it happens like we do for, say, a passion fueled rampage or a drunken rampage.
If you mean people getting desperate because of a crippling addition so that they try to harm others in order to get access to their drug then I'd recommend spending a fraction of what we do going after and incarcerating these people and get them medical help with their addiction and the basic necessities of survival. And if they continue breaking the laws against other crimes, than prosecute them for those crimes.