I think the more important question is if people are literally using it as a debit card, never charging more than they have and paying it off before they have to pay any interest, and there's a benefit to using it (whether it's rewards or better credit in the future in case of emergencies), why is it a bad idea? Most people have enough self control to not spend more than they have so the "chance" of them going ~crazy~ isn't really an issue.
I try to plan my life in a way that if things went catastrophically wrong suddenly, I would be able to land on my feet. That means getting good credit even if my income is enough for whatever I want, saving money even though I don't need it yet, making purchases designed to last long-term even if the short-term option is cheaper upfront, and making sure that I can rely on myself in case someone else won't or can't pull through to help me out. Ideally, my credit will never be an issue, I'll keep my nest egg in a bank account without needing it, nothing I own will ever break down before I get what I need out of it, and people will always be by my side to help me out. But real life doesn't always work that way, so it's only logical to do all you can to cushion a blow.
No effort + no extra cost + no risk + increased security = a good deal.
