Not Bad, for a Crap Idea
Operation Robin Hood will hurt the charity, not the banks.
The card holders will complain to their issuing bank that they never donated.
The bank will check with the payment provider, who will check with the merchant (the charity) and ask for proof for the transaction.
Unable to provide proof, it's a fraud after all, the payment provider or issueing bank will issue a charge bank.
Charge backs a) a waste of time, b) incur fees/penalties for the merchant, and c) the merchant, sorry, charity, may stop accepting credit card donations for (a limited time | ever) as a result.
The bank is used to handling high volume challenges of this sort. The merchant is not.
Good idea. If you're trying to do a DoS on the chary, that is.