I see that some people now compare the growth in value of the bitcoin with the dot.com bubble on the stock markets and the tulip mania of a little longer ago. These are comparisons that, in my view, do not apply. Cryptocurrencies in general and the bitcoin in particular are not a share and not a product but a development. It is a development that is more comparable with the development of the Internet and the development of mobile telephony. I remember that some 25 years ago many people said "Internet, why should we have to use that?" And "why should we need a mobile phone?". Those were people without vision and that kind of people now says "Bitcoin, that's a bubble". The people who do understand the possibilities of cryptocurrencies already had bitcoins last year and they have now made a 1500% return. It is in particular economists who have great difficulty in apprehending this paradigm in their field of knowledge.
If you are not yet convinced by the above then I have another argument: In general a bubble can only burst once. If bitcoin is a bubble we have seen it burst in 2013 already.