why are we still fighting the drug war?

i was just reading an article about the state of the drug war (http://news.yahoo.com/s/ap/colombia_us_drug_war_woes) and, putting it mildly, it is not going well. soldiers are being caught smuggling cocaine back to the u.s. and selling arms to rebels. also, despite "massive aerial fumigation" coca crops actually increased this past year.
when are we going to get it? people like to get high and will pay good money to do so. because of that it is incredibly profitable to sell drugs, so people will take risks because the payoff is so, well, high. i mean, even if you were able to cut the heroin market in half by arrests and fumigation and whatever, that would just make the price double and certainly someone will risk going to jail in order to become a multimillionaire.
meanwhile, we're locking people up for like fucking marijuana possession. who gives a shit if someone smokes weed? if someone is stoned they are probably less of a threat to society - what are they going to do, terrorize the world with their cheeto-breath? drive really really slow?
with all the monetary problems are country has it mind boggling to me that we spend BILLIONS of dollars on something most reasonable people know has about a zero percent chance of working.