Would a truly free society let people do what they want and trust in their abilities to make the right choice?
Depending on what you mean by "free," I'll tentatively answer yes.
How can a person truly be free, if they willingly surrender their minds and bodies to addiction?
Because no one else is compelling them to use the drug. Freedom does not mean "absence of compulsion;" if it did, no one would ever be free because everyone has an internal compulsion to eat, drink, sleep, defecate, urinate, and flatulate. Freedom is the absence of other people using force to compel you to undertake an action; nothing more.
There is no such thing as a truly free society, because a society cannot function without rules of conduct, without law.
Well, that depends on what you mean by "freedom." But one could argue that liberty is the state wherein a person has complete freedom to undertake any action that does not violate other peoples' rights, with only such actions that violate others' rights being illegal. Ergo, you can have a society based upon the principle of liberty -- and such a society would not ban the use of any drug.
Could such a society last? I dunno. The "harm principle" -- only banning actions that violate others' rights -- has never been implemented.