We use most of our brains, just not all at once. There is a purpose for ever part of our brain and we use almost 99% of it, just not at once. Plus each part of your brain can make a different feeling or emotions or heart rate, etc etc, by how the neurons are aligned. Drugs are good because they can give me a crazy feeling, so they stop me from raping and murdering...
Its all what you want to believe yourself. Good or bad, depending on your own belief system. Fact remains that they are out there, and that I used them often, and am somehow still attracted to them.