For example, if im a government and i want to build a railroad, why i need a loan from central bank? I can print my own money without loan, without interest and build the railroad.
Tell that to Germany in the 1920s. They thought they could just print all the money they wanted to pay off all their debts and it lead to hyperinflation. The more money you print for no reason, the less it's worth. That's the problem with your concept of "free money for everyone." If you just print money for no reason - if the money isn't linked to any actual value that has been created - then it is worthless. Money has value because it represents something that already exists that has value.
Not just Germany, countries all over the world suffer from inflation. You have cases of hyperinflation popping up now and then.
Apart from Germany, Zimbabwe is a good example. Leaders can easily destroy countries by their recklessness.
Yes of course, Germany is just my go to example because people don't generally equate hyperinflation with the western world. I actually bought a 100 trillion dollar Zimbabwe note on eBay as a novelty. The currency had more value for westerners who thought it was cool than t did for anyone trying to use it as a currency.