"Black markets are free markets, my friend." So, child pornography, untraceable guns, drugs– are a good thing just because they represent freedom? Imagine your kids getting into heroin because it suddenly became accessible via Bitcoin. No thank you, I don't want to support this future and this type of economic freedom. I'd rather pay my taxes and account for my money if I had the choice to support black markets or lose my freedom.
Thankfully, again, I do believe that there is a middle ground here and nobody will have to make this type of choice.