I sure respect your decision. It keeps life simple. But your logic is bizarre.
You have mentioned "interest rate" as your driving force. Nobody keeps Cap 1 for low interest rate. And You don't sound like the kind of person who would ever carry a balance. Lots of credit unions (like mine - BECU in Seattle) offer high lines of credit at 6% interest rate for those with high scores. No annual fee. As someone else said, Barclay Ring is a fixed 8% for those who want the ability to carry a balance. If you are willing to take a 30 to 50 point FICO hit for the "convenience" of one card that's great. And it's good your spouse has extra cards At some point you will be out to dinner with a client and your card will get declined due to some bank error -- or you will be on vacation in another country and find they do not accept visa or mastercard (I had this happen in Costa Rica). Or you get pickpocketed on the subway and you don't have an extra card in the safe at the hotel. Or you run the card through the washer and dryer as you are racing out the door for your vacation.
Having one credit card in your credit card portfiolio is like owning one company's stock in your retirement account. Not very smart. I sure hope you bought Apple or Google for your one stock!
But hey, you're a big boy (or girl). It takes guts to take this kind of risk!
