Example A. True story. I travel to a different state. I go to make a purchase. The card doesn't work. I call the number on the back of the card. I then have a total stranger on the phone tell me where when and what I purchased for the past week. I can't even remember all that. Now why do I want total strangers to be stalking me 24/7, knowing all my purchases, where and when? Imagine how much total strangers know about me! They know where I like to eat, what I like to eat. What I like to wear. What my tastes in movies and music is. Whether I am an introvert or whether I am an extrovert. The list goes on and on. They could probably have a sketch artist draw a picture of me and they could probably be very accurate.
And that doesn't even touch any of the other reasons - for paying interest, credit reports, reporting and flags etc.
I hate credit cards. I really hate credit cards. I will be following the lead of Elwar as soon as I can!
Well you could get an anonymous debit card to use if you were worried about being tracked or everyone knowing your business. I think regular debit cards have their place though, and sometimes the convenience is worth a little sacrifice.