The amendment procedure allows it to be fundamentally altered, not lightly, but without great difficulty if the people are in consensus about the need for the change. In this sense, the United States actually has what reformers elsewhere have claimed to have: a permanent revolution.
Hence, people who want to call a new convention to create a new Constitution seem to be badly informed about the nature of the Constitution that the United States already has. Any change that enough of the people want can already be made, so long as it does not violate people's civil rights. American respect for such rights is so pervasive and fundamental that a majority of the people simply will not support a proposed amendment that would violate those rights, even if they themselves agree with or would benefit from the specific change that would be made.
Aside from amendments, the Constitution also allows for great flexibility in how it is to be executed and interpreted; in modern parlance, it establishes policy, but does not dictate strategy or tactics. As a result, many aspects and structures of American society and government have almost Constitutional authority, even though they are not spelled out in the Constitution. Working out these structures over the years has been a major way in which Americans have learned from the on-going experiment that is American democracy.
People now, being unfortunately uninterested in history, do not notice some of the fundamental ways in which our society has been changed by our Permanent Revolution during the last two centuries. One trend has been to steadily expand suffrage and direct participation in government, as it became clear that the government actually functioned better if suffrage were not restricted to wealthy white males. Expansion of the franchise to the working classes around the time of Jackson, to freed slaves after the civil war (although, of course, after the end of Reconstruction...
The United States Government. (1969, December 31). In LotsofEssays.com. Retrieved 19:34, April 18, 2015, from http://www.collegetermpapers.com/viewpaper/1304050445.html