That's an easy one.  The true value of bitcoins to a person who wants to make illegal purchases is the ability of bitcoins to be used for any transaction, however shady, with total safety.  There are a lot of people in this thread who want the goods on Silkroad and consider Bitcoins a means to that end - that is, they consider the Bitcoins only virtue to be unrestricted transactions for any good or service, however the legality.