By Mike Dorf
During his recent trip to Asia, President Obama endorsed the idea of adding India to the permanent members of the UN Security Council. As the world's second-most populous nation and its most populous democracy, India certainly has as much of a claim to permanent membership on the UNSC as, say, France, but of course, the Security Council's permanent membership is not determined by a rational calculation of current worthiness. Indeed, giving India a permanent seat on the UNSC would itself call into question the legitimacy of the other permanent members.
Even after the PRC was substituted for the nationalist government in Taiwan in 1971, the permanent membership could still be rationalized as a historical legacy: The victorious allies in WWII were the logical parties to guarantee the security of the post-war world. China was one of those victors and given how close in time the Chinese civil war was to the end of WWII, and given the cooperation of nationalists and communists in fighting the Japanese in WWII, the PRC was a legitimate choice as the heir to the original China seat. In lawyer-speak we could even say that the substitution of the PRC for the RoC was "nunc pro tunc" (retroactive). But if India is added to the UNSC, then there will be no good justification for including France and the UK but not Germany and Japan, not to mention Brazil and Indonesia.
Of course, as a practical matter, the real obstacle in that "etc." is Pakistan and much of the Muslim world, which would view seating India on the permanent roster of the Security Council--and thus giving it a veto--as taking sides in the ongoing conflict between India and Pakistan. Now there is quite a lot to be said for representing both sides to a longstanding important conflict. There are good pragmatic reasons why the Security Council should not act unless there is a consensus for action among the world's major powers. Thus, if the price of giving India a permanent seat is also giving a permanent seat to Pakistan (or Indonesia, Bangladesh or Egypt), that may be a sensible decision.
Of course, so long as permanent members of the Security Council have veto power, the effect of each addition to the list of permanent members is to make Security Council authorization of any given action more difficult. We will end up back where we were during the Cold War when the Security Council was largely impotent (except for authorizing action in Korea, due to the Soviet boycott at the time).
We might even worry that an indirect effect of broadening the Security Council's permanent membership would be to undermine international law. The more difficult it is to secure Security Council authorization for action, the more likely countries that, at the margin, would prefer Security Council authorization, will instead simply act unilaterally.
These factors lead me to conclude that although the Security Council as it exists is a very flawed institution, widening its permanent membership would likely make it even worse.