I am not convinced that the expression ‘just war’ represents an actual impossibility, although I suspect a notion of ‘justifiable warfare’, perhaps borrowing from the legal concept of justifiable homicide, would be easier to make sense of.
But in any event, I don’t see that the idea of ‘Responsibility to Protect’ (RTP) dreamed up to justify humanitarian military interventions was ever likely to work in most cases. The critics have a good point in general that abstract arguments put about the justice (or injustice) of military action can easily ignore history, economic structure, and politics. Indeed, a sense of history and sociology should make clear that tribal and/or sectarian societies like Libya, Afghanistan, and so on would not readily convert to modern liberal democracies! The critics might add, however, that just war theory needs to accommodate power itself – if a nuclear-armed superpower commits abuses against its own people or destabilises others, do we really think the ‘international community’ would even be capable of claiming RTP and invading it to secure a new regime there?
There is a further downright moral problem where shaky justifications and intellectual naivete about war in particular is concerned. It becomes entirely possible for anyone who nakedly ignores moral considerations in their policy making to acquire a perverse respect, and even moral authority. We are familiar enough with the idea of Realpolitik as ‘realist’ and ‘realistic’, which is a sort of compliment in itself. But it is not so unfamiliar for politicians who talk of sticking purely to their (country’s) interest to be described as ‘refreshing’ and avoiding hypocritical cant. In short, they are being credited with being more honest.
This a particularly dangerous instance of the general problem about moral arguments for anything: we need to be sure they (a) stand up against sceptical criticism; and (b) we are prepared to follow where they lead, however uncomfortable. There is nothing worse that declarations of principle which prove impossible to apply in practice.