first of all, as someone said, how old are you?
my personal opinion is that drug use at a young age (18 and below - a rough generalisation) is not a good idea. there are lots of reasons for this - your poor growing brain, maturity, etc. we grow up craving responsibility...
your parents care for you more than anything else in the world, and thats why they're 'overreacting'.
the truth is, the path they describe to you DOES happen to some people, and you can't predict that it won't happen to you.
when i began drug use, i did a great amount of research, like you've done, and i became vastly over-confident in my drug use (under the pretense that i knew the risks and wouldn't fall into addiction, or OD, or whatever). looking back, i could very well have fallen onto the wrong path. i'm just lucky i didn't.
perhaps you could explain to your parents that while you both don't share the same perspective, you want to be independant, and as such, if you wanted to continue your drug use, you will. however, i think your parents have the right to know when and where you are going to use drugs.
that said, most parent/child relationships are unfortunately not built on complete honesty (mine isnt).