yes when bitcoin was first launched it spreaded like a virus into the whole underworld where it has the complete place for all type of illigal activities and more but thats not truly our point. tor nretwork has many sites running and most ofvthem accepts bitcoin as payment
If credit cards and other cards have been sold and used there and being banged, what more with bitcoin, there is nothing governing it and almost no restriction on where you will use it, as long as both party are willing to use it. But anyway, as mentioned so many times before, bitcoin is like an alternative to real life money.