This way you deny them their main source of income: the possibility of
charging interest on you.
You're naive and funny. You want to give them a free loan, and think that you're doing something bad to them. Really? Is that what you think?
The main source of income of the credit card companies is not the possibility of charging interest on you. How possibility can be a source of any income at all? No. Their main source of income is merchant fees. Interest on you is something they enjoy having but can live very well without (they wouldn't give grace periods otherwise, would they?).
You need to understand that if you pay off your statements in full every month - you can only benefit from using your credit cards. You'll be getting (instead of giving, as in your plan) a free loan, and you'll be getting additional benefits such as rewards, cash-backs, and the convenience of aggregating and managing your charges.
By the way I even heard examples that credit card companies closed
accounts for prompt payers who payed their balances in full every
Indeed strange. I don't know what's going in Eastern Europe, but in some other places where I've lived charging interest on credit card is such a rare occasion, that most people don't even know that such a possibility exists.
Why it's such a stupid world that you actually need credit to hire a
car/book a hotel if you are against the institution of credit?
Because when you hire a car or book hotel, you're opening a line of credit. You're allowed to use their property, watch their movies, use their phone, destroy their bathroom and steal their towels. If you don't give them your credit card ahead of time - how can they be sure you're going to pay for all of that? Some places allow cash deposits with additional assurances for those without credit cards, but you have to understand that you have to put something to back that line of credit that you're getting from the hotel/car rental company.