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When spending, you're circumventing fiat. You're participating in a circular, Bitcoin economy. KYC-free and without taxation if you so choose. That's a big difference.
Yes, you are right, it is an optimal way of spending and if we had an option to do so in everyday life I'd prefer to use bitcoin and may be some other cryptos mostly every time I buy smth. But main problem that at the moment I can spend bitcoins directly rather rare... so there is usually a choice between not spending at all or exchanging to fiat and spending. As bitcoin is still money you just spend it when you need as you can at the moment, right?
I think Bitcoin is very necessary for us now. Because the price of bitcoin is increasing a lot. We will see that those who can hold bitcoin will make a lot of money from this bitcoin after a few days. In that case, what we have to do is to try to hold bitcoin. And if we spend bitcoin now, then for us. I think it is a great loss.