The problem is that most people lack discipline and run up debt. Using CCs is fine if you are extremely disciplined.

Dave Ramsey made a career out of teaching “normal” undisciplined people how to avoid and eliminate debt and that includes the advice of “never ever use credit cards or get loans.” A 15 year home mortgage with 20% or more down is the only acceptable debt in his eyes. (And that’s because human nature often leads people into debt, not because of any mathematical basis.) For the majority of “normal” people, he’s right.

We don't spend nearly enough time in primary and high school teaching practical personal finance. For many people that could be the single most important life skill they learn in 12 years of education.

You keep trying to make this "keep your money invested for a month" argument but without actual numbers I don't believe it. How much are you spending in a month that you actually get any kind of investment return on it? And what is your return?

> Why would you want to use the money you have when you can take a free loan until the end of the month?

Because it's usually not free. Most banks charge some fee for providing a credit card. Debit cards are completely free with most banks.

You should really shop around! In Europe I have a free credit card, with a large line of credit, that I literally never pay any interest on, that (used to) fly me to New York in first class once a year on normal household and business expense spending. They're out there - you're throwing away money by not using them.

In the US it's easy to get a zero-fee credit card. Most have rewards programs.

The personal finance advice I've heard is not "don't use credit cards" it is "don't carry a balance on credit cards."

Carrying a balance will eat you alive on interest. As will fees for late payments or going over the limit. If you have the self-discipline to not do those things, there's no reason to not use a credit card.