Well man to answer your questions bitcoin aint criminal money. It's just that some criminals use this currency to buy weapons, drugs and many more at the deepweb. I think that many of the criminals use cash not bitcoin only a small percent of them use bitcoin to buy weapons its just that the media make bitcoin look that way to those who don't use it since the only thing they can see is the bad uses of criminals to bitcoin.
ANY currency in this world can be used for criminal activity. There's absoluetly no difference - the Bitcoin being anonymous and secure doesn't mean all criminals are using Bitcoin. There are criminals doing this for sure - we can't prevent it. People are buying weapons and drugs with cash too.. it's just the criminal's prefference.