I've seen loads of topics of people trying to sell things and saying I want x amount of dollars worth of BTC. Surely if someone is so keen on the idea of Bitcoin fiat shouldn't even be mentioned.
They should be prepared in certain instances to take a fiat loss for their beliefs.
1 some people do take small losses on purchases because of the principle
2 Those with the eventual objective of an all bitcoin economy have to initially deal with the reality that while getting to that point it takes time for all the things they need/want to purchase to be available in bitcoin only.
3 During that process a fiat/$ reference allows them to estimate relative value in the existing economy...eventually the reference can be purely bitcoin..but of course if fiat still exists it will always be compared
4 why not?....freedom of choice.. not everyone interested in bitcoin share that principle but many do.