The Tulipmania comparison is annoying for sure, but here's the thing; it is quite possible that at some point in the future Bitcoin will lose its value for whatever reasons. It could become worthless or worth very little quite quickly or on a gradual decline, and if it does, all those naysayers will spout "I told you so". USD or GBP could tank quite easily or lose its value quite quickly, especially with banks printing more and more money willy-nilly. Paper fiat money is just a piece of paper at the end of the day, just like Bitcoin is bits of code and currencies are only ultimately  worth what people are prepared to pay or purchase with them.