Its funny how when an economist is asked why the value of bitcoins is disputed, they just seem to point to other economists for answers. :-P

In any case, anything only has value as long as people want it. For example, gold has value because people covet it, and its supply is limited. Same is the case with every other "precious" metal out there.

If one fine day, the people of the world decide that they don't want or like gold, then the value of gold will drop drastically. When, eventually, the world supply of gold runs out, the value of gold will rise as people want more of it, and the only source is institutions which have hoarded it.

On similar lines, bitcoins have value because its advantages over traditional money make people want it. Since we know that the supply is limited to 21M, its value will rise as more and more people want it and as long as demand is more than supply.

As more and more real-world businesses start getting involved with bitcoins and other virtual currency, more and more people will get interested in it. As that happens, its value will continue to rise.

PS: I'm not an economist. They are brilliant people who understand the world of money in a way that I cannot even comprehend at this time. What I've stated in this post is just my understanding of how things are.