James Angel of Georgetown's Finance Department and Douglas M. McCabe of Georgetown's Management Department have written The Ethics of Payments: Paper, Plastic, or Bitcoin? Here is the abstract:
Individuals and businesses make billions of payments every day in various forms. Payers have choices about what forms of payment they will make, and payees also have some flexibility on what they will accept. Different forms of payment involve different costs and benefits for both the payer and the payee. Can it be unethical to use a particular form of payment? Can a payment system like bitcoin be “evil,” as charged by Krugman (2013)? Or does it provide a means for a more trustworthy means of payment? What are the ethical implications of paying workers with one form of payment, such as a fee-laden payroll card, over another? What are the ethical implications of choosing a payment tool, such as a rewards credit card, that imposes higher costs on the merchant? The differential nature of bargaining power between the users and operators of the dominant payment networks also raise ethical questions regarding the fairness of charges in such asymmetric power situations. A payment system, like any tool, is not “evil” by itself; it is the use that matters.