Just a brief quote today, from John Rawls.
"To say that a political conviction is objective is to say that there are reasons, specified by a reasonable and mutually recognizable political conception (satisfying those essentials) sufficient to convince all reasonable persons that it is reasonable."
Yes, in context Rawls had also listed the "essentials" to which he makes reference here. But we don't need them for today's point. I think this illustrates the sort of circular reasoning to which constructivists in moral philosophy often fall prey.
This is part of the argument behind his theory of justice as a matter of the principles that would be adopted behind a veil of ignorance by, yes, reasonable people.
The problem is that such work ends up presuming in a word like "reasonable" the whole of its eventual conclusions. So ... my theory is in accord with reason because it is the one with which reasonable people would agree. The people who do agree with it are known to be the reasonable ones because ... obviously ... they agree with my theory!