If it's finite supply then it's a "zero sum" game. Possible to operate an economy on zero sum game ? In that environment, one will need to spend more effort and resources to earn it. Someone's bank account will have to shrink in order for one's account to expand.
WTF does zero sum game go to do with? There is ... zero difference between Bitcoin and paper/electronic money. Both can be used to handle transactions and both rely on the holder to have faith in it.
Just imagine between you and I at a macro level. In a finite world, both account cannot grow at the same time and negative balance does not exist. Once one account reaches zero, everything stop.
It's the first movers' advantage. Those who have bitcoin will have a lot of US dollar. 21 million not enough ? Then have a pico satoshi.
Just imagine Bitcoin goes higher and higher .... like it has done since Satoshi or tRump or whomever coded it. Wait we don't have to imagine (well maybe the Orange Jesus part) since that is its history. No zero sum. Although nothing is ever guaranteed in life. Now on the flip side let's imagine the dollar goes lower and lower in value. Wait again, that is its history. And someday that will be a a zero sum ... game over. Have a good weekend.
I borrow from President Bush. If that sucker ever to come, we probably need to go back to barter trade.