Whether or not the war on drugs is useful or not isn't for me to determine. Drugs are illegal, and my job isn't to try and justify the war on drugs, it's to get the drugs off the streets and apply the law in a fair and equal manner. If you don't like the war on drugs, don't take it out on cops, take it out on politicians and have them change the law.
What you have just done is called the Nuremberg defense because it is the same excuse that the Nazi's gave during their trials for crimes against humanity. Following orders and/or the law is NEVER an excuse for violating people's natural rights.
Anytime you arrest someone for just drugs, you are committing acts of armed robbery and kidnapping against people who have not violated anyone else's rights.
The fact that you wear a badge does not change this. The fact that the state says it is illegal does NOT change this. You are an individual with free will and YOU have a choice in the matter.