What are you talking about? What do you think, who builds the streets, public buildings, schools, universities, hospitals, etc.? Everyone who works and pays taxes contributes to this.
Once you convert your coins to Fiat, you have to pay taxes. How much tax you have to pay depends on where you live. But it also depends on the value in which you convert the coins.
In some countries, you only have to pay taxes starting at a certain limit. For example, if you have converted $ 10,000 worth of coins, and the specified limit is $ 6,000, then you have to pay taxes.
But if you are underneath, you do not have to pay anything.