The drug addicts create the demand for drugs, and no matter how many drug dealers you'll waste, new ones will come if they can profit. The root of the problem are drug addicts. Right now in the Philippines, drug dealers along with drug users face zero-tolerance shoot-to-kill punishment, and it's an amazing success with thousands of arrests and/or executions since it's start 6 months ago, and drug cartels are cracking, to the extent that very rich and powerful mayors and politicians who have links to them have surrendered to the police.
From a moral perspective, the drug addicts committed the sin of indulgance, the drug dealers of violence and greed. In democracy, indulgance is not considered bad, so according to our society, you can only blame the drug dealer, and that should be our policy if we want it to be consistent with our other laws. Whether you think indulgance should be punished or not is what separates ideologies.