Part of the demand is pure speculation, people who just buy Bitcoin with the hope that it increases so they can sell it for a higher price later on.
Another part of the demand for Bitcoin are people who actually need Bitcoin for its uses.
I reckon that a pretty big part of the Bitcoin economy is driven by people who use Bitcoin for illicit purposes.
Perhaps it's not something we'd like to acknowledge, but it's certainly part of the demand of Bitcoin and without it, prices would be lower than they are now.
Darknetmarkets might even have jumpstarted the initial demand for Bitcoin, I'm not sure what kind of effect it has now on the price.
Let's not forget the legal uses, people might also buy Bitcoin to send money overseas or just because of ideological reasons.
That's right, part of our need is a bitcoin in the hope that it will grow and sell. But our needs are just a small part of Bitcoin's demand for illegal trading. That is absolutely undeniable, so that the price of Bitcoin can be so high. I fear that, they will gradually give up Bitcoin to seek a better way to trade, a new currency