A lot of people are only interested in crypto-currencies for use in the black markets. While probably a majority here are more interested in them from a computer science or investing perspective.
It seems that they're mostly currently being used for speculative investments (not a particularly good use for a currency) or for black market transactions.
Can you give some examples? I'm not sure what you mean.
Same with marijuana. I live in a US state that's legalized it, and every shop requires cash payment because no payment processor will talk to them.