That is so stupid humans don't operate off of constant logic, we are constantly influenced by on a whim emotions and changing ideas. Also people are commonly illogical. So let's say we make prostitution legal, what happens when those prostitutes start getting murdered? What happens when the rate of STDs go up because more people are ya know, doing the same tute? Laws keep people from doing stupid things by providing a punishment to deter it. Now you may make the argument "Well the guy should know that he is at risk." What if he is not given the proper education on the subject, or possibly it slips his mind?
The right to suicide is also a terrible belief. What about all the teenagers who commit suicide for extremely petty things, (my girlfriend broke up with me, my dog died, I got an F, nobody liked me today). Normally I could call the police, who will have the clearence to come in, arrest, detain, and rehabilitate or help that teen or adult. Now under your laws, I could call the police but they could not do anything about it and now I'm short one friend. Additionally you have people who overdose without knowing the consequence, and people who become depressed over a large event that doesn't warrant death (divorce, family/friend death,, or presidential election) the latter going off an illogical idea that "This is the only way out"
I agree with rec drugs, not hard, but certainly pot.
I don't mean to say the government knows best, but the people in it are more educated than the common man and there are scientists who work for the government in all fields.