When an anti crypto advocate uses drug trade as an argument, kindly direct them to this old article.
90 percent of U.S. bills carry traces of cocaine
-100 percent of bills from a few large urban areas tested positive for cocaine
-The average US bill stays in circulation for 20 months
-Although the contaminated bills do not affect health, they could cause a false positive drug test if a person handles contaminated currency repeatedly (for example a bank teller)
http://www.cnn.com/2009/HEALTH/08/14/cocaine.traces.money/
90 percent of U.S. bills carry traces of cocaine
-100 percent of bills from a few large urban areas tested positive for cocaine
-The average US bill stays in circulation for 20 months
-Although the contaminated bills do not affect health, they could cause a false positive drug test if a person handles contaminated currency repeatedly (for example a bank teller)
http://www.cnn.com/2009/HEALTH/08/14/cocaine.traces.money/
Those are pretty incredible stats. All forms of currency will be used for illegal activities, it is inevitable. In fact, cryptocurrency inherently makes it more difficult to hide your identity from authorities, because you eventually will have to spend your coins, leaving a traceable foot print. In the early days, people who used cryptocurrency to purchase on the black market websites, probably didn't realize this.
There are still too many people that have misconceptions about blockchain technology, which could delay Bitcoin in reaching its full potential. Like you said, all forms of currency will be used for illegal activities, so it isn't a valid argument against cryptocurrency. Even the most anonymous cryptocurrency, is no better at hiding illegal activities than cash.
Indeed, it takes a lot of effort to fully understand the technology in order to make your own decisions as what makes sense and what is propaganda. Maybe by explaining what is propaganda and why we can get people to take a closer look.
