There is no real easy answer to this ...
There are some fairly well known drugs that are illegal for some pretty arbitrary reasons, but the majority of illegal drugs because of how highly addictive, dangerous and destructive they are. At the same time you have to consider that making something illegal doesn't seem to prevent people from having access to it, and there are countless ways for people to use similarly addictive, dangerous and destructive that can never be made illegal to get high.
My personal belief is that we should first create less arbitrary reasons why drugs should be illegal, and criteria surrounding how addictive a substance can be and how easy it is to overdose should be established for determining which drugs should be illegal. The second step should be to fight the (moronic) mindset that our society has where we believe that we can fix all of life's problems with drugs ...
