Offer your thoughts or opinion on the input financial query or topic using your financial background.

Could one person with a card with no spending limit pay off everyone's debt? 
The problem would not only be that of Kyle but also that of American Express. When Kyle pays by credit card, American Express pays the bills out of their pockets on his behalf and then forwards the bill to Kyle. The issuer of a credit card takes the risk that the holder of the card won't pay the credit card bill. In practice there are safeguards in place which prevent a company like AE to pay such huge sums in one day through an automated process. Credit card companies have sophisticated algorithms to determine unusual spending patterns and block any transactions which appear unusual. Also, after a few billions their bank will likely block them and prevent them from paying any more bills. But let's play along and pretend these safeguards wouldn't exist. That means after Kyle's spending spree, American Express will be trillions in debt, with their main debitor being a 10 year old boy who won't ever be able to pay. Kyle will have to declare personal bankruptcy. There are various variants of bakruptcy in the US, but they basically all boil down to him paying everything he can pay (not much considering that he is 10) and then defaulting on his debt. Afterwards he is debt-free. That means the debt is now that of American Express. American Express will not be able to pay that debt with their bank(s) either, so they will have to declare bankruptcy and default on their debt too. This domino effect passes the burden on to the banks which can not carry a trillion-level debt either. A bank going bankrupt is a serious issue because it means they can not pay back any of the money in the saving accounts hold by companies or private people with them. So the problem would return to those people Kyle wanted to help in the first place. Also, the collapse of one bank will often result in the collapse of further banks, resulting in a collapse spiral destroying the whole world-wide finance system. Nothing would be gained.