As much as I know in the US people use mostly credit cards. I have spend around a year in the US and I knew only students that had debit cards in stead of credit cards. What I am trying to say is that this move will affect the process of buying crypto currencies. On the other hand it seems weird to me that you are able to trade crypto using a credit card. So I find that ban logical because of the risk the banks are exposed to. And I do think that most of the people trading crypto really don't understand the risk.