What if the US Constitution was flexible?

I have a godbrother whom I love very much. He is an annoying little twerp, but like my very many brothers and sisters (blood or adopted), he has been an integral part of my political thinking. He is a Jew, non-practicing, and I am a Christian. I would call myself Pro-Israel, for I am never pro any country. I do love its people but like many other governments, its politics disgust me. I am skeptical and would rather hope that Palestine will be free someday.
My brother is a 16 year old who has grown too fast, and has learned quality music like the Beatles and BB King. In one of our daily squabs, we have started on the constitution. i can always excuse him for not having read the whole document- he is in HS after-all. But he has bought into the whole American-exceptionalism and the menace of the idealism of manifest destiny. However, he is advocating for a flexible constitution. His argument? Things have changed! Apparently, the "founding" fathers could not possibly imagine a world where there were bombs, nuclear weapons, the internent, and spies. I couldn't get past a word to let him know that in those times, all these dangers, maybe with an exception of the nuclear war, were all a possibility or in existince, albeit on a smaller scale.
So I had to wonder if he was not onto something. What would it mean if the US constitution could be flexible? One of the most fundamental values of the US is the Constitution. In fact, it can be said that it is what holds this country together. It is what lawmakers boast about, the platform for many political debates, and the tool for justifying a lot of actions by the government and its people. The constitution is the fundamental brick, in the making and sustaining of this nation. Therefore, arguably, if the constitution was to be flexible, so would this country. The national debate would not be on the Federal government becoming bigger, it would be bigger. The states, well, one can only imagine that with all these states co-habitating under one umbrella, there are those that would have like to sucede. The price to pay for a flexible constitution is chaos. From the preamble, to the last sentence of the constitution, the laws that established this country have seen it come this far. But by all things comparable, the country is still young-Europe is much more like a good, bitter aged wine that takes a lot of getting used to. However, guaranteeing freedom of the people, and establishing the checks and balance system, the constitution has assured that the people have a louder voice in politics than those in the government, and that there can be some form of separation of powers in government that makes it essential in managing the very many facets fo the American system.
Things have changed, and there are things like the second amendment that could use some refining, but to make the US contitution flexible would be disastrous, as the government could claim the power they want, without the censorship of any law. There could also be a Bush dynasty in the making....Think about that. The arguments for a bigger government is just not pertinent. Even with Obama's efforts of a health care upheaval, the country is no where near becoming a socialist government. Even France at its best is not worst off for being a social democracy.