i had a report on the same thing...
some things i used were:


hemp,
marijuana prohibition laws were passed only by propaganada william hearst/anslinger created (search tehse, therye pretty funny),
its medical uses,
alcohol, AWOL (alcohol without liquid) and alcohol are legal and kills so much more then marijuana,
and the failure on the war on drugs (millions being spent on marijuana yet no decrease in usage among teens and adults)