Hehe. Then Exchanges own many coins because users don't have private keys

. They only have email and passwords.
It's unethical for exchanges to steal users' coins.
Spot on, and the question is do we own fiat money on our accounts or bank is the real owner?
Do we own a house or government/state is the real owner, and I can think of many examples like this?
About fiat money and bank accounts, That's a serious question. You are the owner of that money on a piece of paper. Bank/Gov can control your money. Here Bitcoin can resolve the problem. Satoshi created Bitcoin to resolve this problem over a decade ago. I believe he was kind of successful. Slowly but surely the whole world people's will understand the importance of Bitcoin and its facility. Also, limited knowledge can Fu*k up too. If they own Bitcoin on an exchange, it's like you own Fiat on a Bank. Similar issues.
Do not hold your balance on exchanges. Keep them in your wallet.