Short version: If drugs weren't dangerous, they wouldn't be illegal. Period. End of discussion and all the rest.
Long version: Drugs kill brain cells. And before someone says "But tobacco does the same thing to your lungs, and that's legal", I don't get the reasoning behind that, either, other than that: 1) There was a rather long time when people thought smoking was harmless. 2) Even when they figured it out, people were still buying it, and apparently economy matters more than human health. Go figure. 3) Even when they finally realized that there would be no one to buy the product if they were all dead, making it illegal wouldn't change much, if anything. People are still addicted. Drugs are illegal, and some people still do them as though they aren't. There are no good reasons why they should be legalized.
Oh, wait... Isn't this topic about "WHAT IF drugs were legalized?", and not "SHOULD drugs be legalized?" If they were legalized, there would be more people jumping out of windows thinking they can fly. And maybe they would think the same of their pets, and it would literally "rain cats and dogs".
I have to agree with Geno. I mean, I can understand SOME ideas of the drug legalizations- I heard marijuana can be used to treat bad diseases, so maybe they could use it, BUT ONLY FOR THAT, legally; as for alcohol, I...don't really know where I stand on that, on one hand it's religious and the Prohibition really didn't turn out that well. >_>; I don't like cigarettes at all, though, probably because my dad was a smoker for a long time. I understand that they weren't always known to be dangerous, however, so that can slide...and I'm kind of afraid of a repeat Prohibition if they were banned.
My main concern with the idea of drug legalization is that, well, things are usually illegal because they're BAD. Murder? Bad. *crag*? Bad. I know people still do it, but some of them at least get caught and punished, and...well, society is kind of *crag*ed up in that some people THINK it's cool, but a truly good parent doesn't go out an encourage their kid to *crag*. If someone turns down the wrong road, there's always the reason of it being illegal. This, I think, is why so many teens get into binge drinking or smoking early. They take it lightly because it's legal, and then they can slip into the illegal stuff. If you're given the impression that the law really doesn't differentiate between good and bad things, then what's to stop you from doing them?
If they legalized drugs, you would probably be hearing this in your head all the time: http://www.youtube.com/watch?v=7P6iZ5g7gyw But if you start hearing "4000 Degrees Kelvin" playing IRL, run. Or you will *probably* be baked, and then there will be cake.