What would happen if everybody wants to exchange for a real money?
Depends. If everyone wanted to do it at the same time, it would be the same thing as everyone suddenly selling all their TSLA stocks. It'd dump to the ground. If everyone wanted to do it but progreasively, it might not mean a huge dump is incoming. Remember that for any sale there is a seller
and a buyer. It's not like you claim USD for Bitcoins and then throw your BTC to the trash. No. You sell it to someone else who believes in it.
I consider it not fair to mine cryptocurrencies?
Why? Sometimes miners don't even earn as much as they pay for the electricity & hardware.
If it is so good why there is a need for exchange rate to the real money?
Because the world functions on fiat right now and it can't be a currency or a store of value if it has no real value. Value is currently measured in fiat, so.. it's kinda logic from here.
Why recently I needed to block about 30 phone numbers constantly calling me to invest money in cryptocurrency? Is it going to finish soon because of having probblems not to be fed this pyramide game with real money?
If you call this a pyramid game, then I suggest you read about Bitcoin because it's quite clear you don't understand it. Your messages are coming due to your own fault. Giving away personal information for free ends up exactly like this: your data is being sold to someone else or leaked by some hackers who obviously have no good intentions but to do phishing on you.