Banning credit cards is totally acceptable. It is the banks money you are spending and if they worry that they don’t get it back then they won’t let you do this. Banning debit cards on the other hand is unacceptable because it is your own money and the Bank has no reason to block this.
The solution to these problems would be peer to peer exchanges where you trade directly with the other person that holds the Cryptocurrency. Banks can’t interfere in these transactions.