first of all you can not overdose on marijuana (unlike alcohol), so there really is no "excessive use". also "psycotics" are rarely added to anybodys stash, thats just bad business.
second of all, if legalisation occurred, drug dealers would be OUT of business, not given political power. everything would be state/federal regulated. ~700,000 people a year would not be arrested, giving police more time and energy to focus on better issues. the $30 BILLION dollars spent every year on the drug war could be better spent on say, oh i dont know...EDUCATION (whos funding was cut here in kentucky recently, not sure about anywhere else)?
what it all comes down to is drugs need to be treated as a HEALTH issue instead of a PUBLIC SAFETY issue. treatment is a better method than incarceration.