you don't "need to" buy bitcoin with fiat, you "choose to" buy it with fiat. it is like saying you "need to buy US dollar"!!!
the real way of gaining bitcoin is to getting paid for the work you do just like the way you are getting paid in US dollar (or any other fiat you get paid in if you are in another country).
Correct me I'm wrong, the way I understand Bitcoin, the real way of gaining Bitcoin is thru mining. I think trading, and getting paid with Bitcoin is secondary to it. Besides, if the one paying BTC is not mining or buying it with fiat, they won't be able to pay us with BTC.
In the current situation, I still believe that fiat is more important than BTC in a day to day transactions of a normal citizen.