It shouldn't have been built, but for other reasons - the biggest one being the enemy for which they're designed to fight is not who the US military is likely to be dealing with in the future.
What role do these hyper-advanced aircraft have when you're fighting Al-Qaeda, ISIS, or whoever the stone-age-terrorist-du-jour is? We're not going to be fighting China, that's for sure; both they and we are way to inter-dependent.
So sure - the money already spent is sunk cost. But why throw good money after bad?