RBG's basic idea is 1) the Constitution is dated and 2) that there are newer ideas we can glean from.

Firstly, at least as read one way, the first assertion is highly debatable because the principles of limited government, the checking of abuses and preventing tyranny through a careful system of checks and balances, the independence of the judiciary, the inability of the majority to rule on certain things (the Bill of Rights), etc are all timeless ideas. Their codification in the Constitution was the result of much political philosophy, deliberation and debate. It was also informed by history.

The Framers understood that 1) they had no guarantee that future people would be as wise and virtuous as they considered themselves to be and 2) democracy, while preferable to other systems of government, carries with it the risk of mob rule or tyranny of the majority. As a result, they drafted a written Constitution which, if ratified by the states, would serve as the legally binding document which prescribes exactly the manner in which the government encounters the individual. The rules set forth the structure of the government, how power is distributed among the various branches and how those powers are checked in order to maintain the primacy of the individual.

To put it simply: given that

a) the Framers thought very deeply about all the problems associated with this system of government and the best ways to resolve or minimize those problems

and given that

b) they had no way of knowing if people in the future would be as cautious, careful and diligent as they were in their thinking

and given that

c) mistakes and poor thinking in these matters tends to disfavor the individual whose rights they sought to protect

that therefore amending the Constitution should be very difficult and it should require an incredibly high level of agreement and consensus that can only be achieved through an abundance of deliberation, argumentation, etc. In other words, the system they designed which was so carefully considered should not be easy to change. The system simply isn't durable if in order for it to work, we must have faith that every generation which might come to adjust the system is at least as virtuous as the one which ratified the Constitution. On the other hand, the Framers were not so presumptuous as to think that they could have anticipated the needs of all future generations so it simply had to be possible to amend the Constitution under some circumstances. The high bar for ratification offers some protection against the risk that by bending to the passing political whims of every generation we bring about the disintegration of the system.

Put another way: the protective nature of the Constitution -- against government infringing on individual liberties, on the government devolving into tyranny, etc -- is inversely correlated with how flexible the system is.

_We_ might consider _our_ amendment aspirations to be good and virtuous and well-intentioned, but the power to amend does not go away when a new group of people who are less well-intentioned arises. Hence, the great difficulty of amending the Constitution hampers the bad actors, even if by so doing it also impedes "progress" sought by good people.

RBG doesn't seem to understand this or, at the very least, her comments quoted here reflect a lack of appreciation for this aspect of the system.