<sigh>. There's a fee free ATM at every Costco checkout, for the very purpose of paying for your purchases. But that's beside the point.
I'm advocating not being a victim. There are no guarantees in life. Cards can be shut off at any time due to any reason: fraud detection, compromised merchant databases, F/R's - lender skittishness, etc. You can get robbed, or simply lose or forget your card at the last place you used it!
Besides, the concept of only carrying an Amex is flawed. Many merchants do not accept Amex in the US, it's worse abroad.
So you can worry about the 1% chance of being in an F/R situation, or you can live your life. Use your Amex. Don't do stupid things like paypal funds to a authorized user. Don't churn coins. Carry a backup (or three).
And if an F/R or any other unlikely incident happens, don't be a victim. Use your backup. And if you "fail" the F/R, face facts. Its 2010 and times have changed.