Of course we have a living Constitution. There are in the document itself amendment processes that can be used to revise and make changes deemed necessary by the citizenry.
But most who use the term ‘living Constitution’ are not referring to changes made according to the well defined methods laid out in the Constitution. They mean that judges will decide what changes are called for and make decisions based on their subjective prejudices. Thus that governments are, ”deriving their just powers from the consent of the governed,” becomes perverted into, “deriving their unjust powers from the consent of a bunch of self-righteous judges who make choices not sanctioned by written law.” And I feel sure THAT was not the intent of the framers.
Just for laughs I’m going to quote what wikipedia calls one of the strongest arguments in favor of the pushy-judges-who-don’t-know-their-place school of Constitutional interpretation. The wiki likes this ‘argument’: “the fact that the Constitution itself is silent on the matter of constitutional interpretation . . . [is] one of the strongest arguments in support of the concept of a "living Constitution" A philosopher would call this an argument from silence. It also proves that judges should mind their own business since the Constitution nowhere explicitly states that judges should not not mind their own business. It is also an argument in favor of Gitmo since the Constitution nowhere explicitly states, ‘Thou shalt not build prisons in Gitmo.’ I trust the reader is catching on that an argument that proves an infinite number of propositions truly proves nothing. And they call this one of their strongest arguments.