The power of the constitution has been used to support those values you champion in ways the founders would not have voted for (certainly, it would not have commanded a majority vote of delegates and would not have commanded a majority, let alone 9 states). But you misperceive the point of a written constitution if you think it is to confine the people of today to the dead hand of the past. Instead, its to ensure the rule of law, to prevent arbitrary action, and to temper the passions of democracy. All of those things are just as relevant today as they were back then. However, they are solved by requiring consensus for change, not by removing change.
There are two (possibly three) provisions in the Constitution that cannot be changed. Even then, there's a good argument that even that can't limit the consensus of the people to choose their own government. After all, that's the only point of government, is to benefit the people who create it.
To quote Jefferson (at least, apparently Jefferson, I haven't verified the quote):
No work of man is perfect. It is inevitable that, in the course of time, the imperfections of a written Constitution will become apparent. Moreover, the passage of time will bring changes in society which a Constitution must accommodate if it is to remain suitable for the nation. It was imperative, therefore, that a practicable means of amending the Constitution be provided.