One, drug use impairs your judgement far more than even alcohol. Try driving, or perhaps just getting into an argument, when you are drunk, then multiply by 10
Two, I am sure I can find statistics showing how many drug users turn to crime to support their habits, and how large a portion of all robbery is drug-related. I suspect that statistics will not be good.
Three, as I already said, US-backed counter-drug operations, since they are in reality carried out by other countries, tend to be very bloody. As an alternative I proposed trying to attack the problem from the supply end.
Four, those innocent bystanders conscripted by a drug cartel and then killed in a raid? They were basically enslaved for the 10 years prior to that because their coca farms can't refine the drug, and they sell it for next to nothing to the cartels, who refine it and make millions.
Five, they cause massive amounts of money and police attention to be wasted trying to uproot the problem. The police are thus unavailable to deal with other threats to civilians.
Only two of these (3 and 5) could be stopped, or slowed, by legalizing drug use. The others will get worse, more than make up the difference. The third one will probably continue as 3rd world countries try to wrest control back from the cartels. More people will die.