Do you always buy everything that's for sale? No buyers and sellers would disappear. So I blame drug addicts for the drug problem. You?

not all the time

I blame users.   If someone wants something, someone's going to supply it - no matter what it is .. legally or illegally.  If no one wants a thing no one's going to sell it (no money in that).
We all like to feel good or, as it's sometimes known, being "high".  This high can come from any number of natural (good) ways - helping others, listening to music, eating, writing, loving (and so forth).  Unfortunately, some people aren't satisfied with these ways of "getting high" (too much work?); they want to get "higher".  So over the centuries, people have  found many artificial ways to get high - smoking plants, licking certain toads, inhaling fumes and, of course, taking drugs.  It was not a supplier who first licked a toad to get high, but you can bet once they found out it was possible that they encouraged their friends to do it too.  Since money is many people's only objective in life, that person probably started selling those toads (and he got rich by doing it).  Before long they were shipping toads all over the world.  Yet before long, this high wasn't enough.  people wanted to get even higher.  So they turned to something else (huffing dung, smoking plants, ingesting secretions, etc.).  And, once again they started selling it to their friends and became rich in the process.  And on it goes - the eternal search for a bigger high and someone getting rich off it.  Unfortunately, some of these "highs" end up killing the user.  But people want that high so much that they're willing to risk their lives to get it.  
The only way to break this is for people not to want to get high - and that ain't going to happen (as I said, life itself is less important to a user).  So as long as there're buyers they're going to be sellers.  No buyers no sellers.