I'm glad you paid it off.
The reason so many of us don't like credit card debt is that interest can be your best friend or your worst enemy. Credit card interest tends to be high - and if you have the discipline to leverage a 0% card, that is awesome and will work to your benefit.....many people don't have that discipline, or like to believe that they will and then find themselves in a hole. As an enemy, interest is an expense every month that sometimes you picked up from necessity, but you shouldn't let it hang around any longer than you need to.
As your best friend, interest (or dividends in the stock market), can add to your income. So if, instead of paying interest, you managed to take that same amount of money and put it in AT&T stock that generally pays about 5% in dividends, you'd do a lot better over the long term for very little effort. People on this board will go to a lot of effort to coupon, Swagbucks, and stack discounts into a little extra money - once you switch from paying interest to investing for dividends, its easy extra money (not a lot at first, but over time it can be quite a bit.)
(Leverage is a different conversation, but it will come up in a conversation like this. Leverage is when you get a low interest rate and then use that money to make more money than you are paying on the interest. A 0% card is leverage - if you have the money to pay it off sitting there being useful. I have my house leveraged - a low interest rate, plus a tax deduction - and that money in the stock market - there is risk, I don't have much of my house leveraged and I can pay it off several times over. You have to understand the risk and your risk tolerance.)
Understanding that, and understanding that young enough to make compound investment gain REALLY work can mean financial security. And a lot of us on the budget board want everyone to have that feeling of financial security. Sometimes people have been a little mean about it. (Sometimes people have been a lot mean about it, but on the other hand, some people have been offenders of amazing self inflicted financial trainwrecks over the years).