1. If your debit card/credit gets stolen, you can shut it off. Cash gets stolen, you're shit out of luck.
2. You're paying with cash everywhere, but only have $20 bucks at any given time?
3. I didn't say my time is more valuable than yours. Our time is equal, which is why it would be awesome if you got up to speed in today's world and stopped slowing everyone down.
4. You don't understand how credit cards work. I earn $100s in cash back every year and pay absolutely $0 in interest and $0 in fees. If you pay your cards off on time every month, there is no interest and the cash back rewards are quite literally free money.
5. Using credit cards in the quickest and easiest way to build credit. Your a silly person if your prefer to do things the hard way.
6. Yeah I kind of stretched on this one. No one disputes in person transactions.
7. You'll know how much you spent in total, but won't know what you spend it on.

No but seriously, point number 4 is the biggest reason. It's free money. And no the interest doesn't outway it because there is no interest if you pay on time. And it much bigger than $0.02.