But you need to get your fiat converted to bitcoin to begin with. Unless you want Bitcoin to only be for the miners or only for people who sell things to people who have bitcoin. In that case it is massive FAIL for bitcoin for anything but a very small niche market. Of course that is what is inevitable because the big Banks will make this happen but it's definitely not a good thing.
That's the point: if the banks will make this happen anyway, no need to continue deluding ourselves.
I think it will not be a massive fail, but the exchange rate will be set against real assets, as it was in the 10k-pizza days, or whatever being sold on Bitmit and such.
More than half the Bitcoins are already out there. So, it's not only the miners that can spend them. If you have goods or services that I want, I'll pay for them with Bitcoin, even though I am not a miner. So, it might just take more time for bitcoins to spread around, but I think it won't be the massive fail you predict.