By so doing, they are encouraging customers to investigate alternatives. If you successfully use bitcoin for these medicines, you might well choose to use it for other purposes. Is this in the interests of Visa & Mastercard?
British Rail used to be a common carrier - they had to transport anything they were able to. They could not refuse on grounds of "we don't want to handle medicines". I feel the time has come for governments to crack down on the power of the big merchant service providers.
(There is just one sort-of let out clause - the buyer protection issues. Specifically credit card issuers do have an argument up to a point with this. But not debit card or paypal or Western Union and similar.)
Havew you ever seen a bank refuse to let you write a cheque? Or a treasury/national bank say you cannot use one of their notes?