The only Constitutional term limits--those on the president--are not philosophically consistent with democracy, but then again, neither is the US Constitution. In practice, because of technology and the increasing expansion of US global power, we've seen a steady drift in power in our government away from the legislative branch and toward the "imperial presidency" of the executive branch.

The general drift of history has made executive action more relevant to public problems than the deliberative processes of Congress. As a result, we have a balance of power in the Republic far more heavily weighted toward the president. The power of the incumbent to get reelected was strongly demonstrated four and a half years ago, when an absolute trainwreck of an administration was able to put itself over on the public by utilizing the imperial presidency.

Add to this the tendency of those in power to become corrupt and less scrupulous of their public duties over time--the well documented year six scandals that plague most presidents--and you can see a pattern emerging of a presidential branch designed to perpetuate its own power and marginalize the other branches. I guess you could argue then that the people should just start being more diligent in their citizenship duties and force the legislature to stand up to presidential power more. The problem is that experience shows that the neither the people nor the Congress will actually do this.

From the viewpoint of practical experience, you need to have some external limits on governmental power where the intrinsic limits of democracy don't do the job. In the case of the US Constitution of government, simple voting isn't doing the job. The 22nd amendment effectively prevents crises of power sharing that might otherwise occur because it creates an artificial limit to how long presidents can spend accumulating power.

Or use this analogy: driving over the speed limit isn't dangerous. If you have the right driver in the car and he can handle it at 90 mph, then why should there be an artificial cap on his performance? Because the regulations don't cover what goes right; they serve to prevent that which might go wrong in a more catastrophic way than what you're expecting.