I don't know about the people in the US, but I can tell you why I want to completely legalize drugs. I see only benefits (less organized crime) with no downsides (I don't think drug usage will increase, as drugs are extremely easy to get even now). Note that the prices don't need to drop - the government could still tax drugs even higher than they tax alcohol and tobacco now - so there's no economical argument why the demand would increase.
