That is irrelevant as I have explained. What it does is reduce the network effects (merchants accepting and holding Bitcoin thus being nodes in the Metcalf law valuation) within the Bitcoin ecosystem that those holding fiat must buy BTC to attain. If everything they can buy with BTC they can also buy with fiat, then there is no great need to buy BTC with their fiat.
That was precisely my point about why lose 3-5% on double exchange, when one can just buy with their credit card for 0%.
Many people prefer to use BTC rather than credit cards, even though they can use either, because BTC is faster and more convenient for online payments. They buy, wait for the price to increase, then spend when needed. It's that simple. I do not think this 3-5% double exchange loss you are talking is a significant factor in whether or not people choose to use or accept Bitcoin.
The 3 - 5% is an ancillary argument and not the core one. If they wish to be irrational and waste 3-5%, it doesn't mean they are part of a trend of new adopters who love to waste money. Whether Bitcoin holders continue to be interested in Bitcoin is irrelevant to the point I was making. I was making the point that if we don't create more merchants that accept only BTC, i.e. hold BTC and not just a useless facade for fiat, then there is no compelling need for non-Bitcoin owners to decide to acquire Bitcoin (if we are speaking about its demand as a currency and not as an investment).