Actually, alcohol and drugs do cause bad behavior. It removes inhibitions, creates very bad judgment, and disrupts the brain's ability to function properly.
Drugs can make people very dangerous, be it directly psychotic (see stories of people on the new synthetic drugs) or indirectly dangerous (getting behind a wheel). Alcohol is the root of many domestic violence situations.
I do think it makes a big difference, and here's why. Using drugs/alcohol is a choice. Sure, it becomes a disease when the body becomes addicted to the substance. But the choice to stop is always there. And I've met many recovering alcoholics and addicts who's "bad behaviors" ended with a solid recovery program and commitment to sobriety.
JMHO.
~T