The obsession with legitimacy is the original recursive argument of political and philosophical debates. It sets off from an ideology of origination that skews all subsequent discussion and investigation. Thus in many ways the appeals to something’s being self-evident is a stunningly original departure (much as the experience of reading Descartes and coming across the cogito ergo sum for the first time). It denies the dominion of the past, saying that our ever-present (N.B.) capacity for thought and invention is necessary, if not always sufficient.
The difficulty with removing legitimacy is that a thing must be allowed to grow and change, lest what it is now become but another foothold for those attempting to climb back to the days of yore in the assumption that older=better. (This is why the argument of a type of infallible, original intent interpretation of the U.S. constitution is the most perverse of all, attempting to be both historical and yet valid for all time.) If we consider a thing to be growing and alive, then this must imply that it will eventually pass out of being. Legitimacy should be considered according to what we want now and in the future, considering whether this tallies with the past. If it doesn’t, why not? If not, do we do away with it?