If nothing else, it's that the users get pulled into some braindead power struggle between two companies that they could care less about. Yet they are the ones who find that they cannot use the products anymore properly. Moves like this decrease the quality of both your product and your competitor's. Yet the whole sense of competition in capitalism is supposedly to increase quality.

Of course that's just the obvious consequences, ignoring the larger implications of allowing companies to place arbitrary restrictions on their services - when at the same time those services become more and more critical infrastructure.