Okay, let's think of a scenario and analysis what will happen if we have a fixed supply token as a currency. Let's think BTC is the world currencies now. In these cases, rich people will buy as much BTC as they can and took them out of circulation. Poor will have little chance to buy any BTC. When most of the BTC will be out of circulation price of it will go out of reach of normal people. The whole world will be in an economic crisis and violation of the law will be common because people will not have any BTC to buy food.

But that doesn't mean crypto can not be one of the world currencies.