I see this as a problem, but IMHO, it's not one that should be solved by limiting interoperability on DW, especially since the desired effect (limit FB users from coming to DW) is not actually something which I think DW should be discouraging? The problem about social links between people who try to segregate their RL and pseudononymous identities, and those who do not is one which pretty much is at the center of social media.

If DW were for example to get a lot more popular (say Thorfinn suddenly convinced people to join it), even without this feature being implemented, the same problems could potentially occur, also. So I guess what this situation is, is that to some the obscurity and 'walled garden-ness' of DW is a feature, and to others, it's a bug.