The problem with a benevolent dictator is that they die eventually, and are replaced by a non-benevolent dictator, or a civil war, or both. Unfortunately it looks like the US democracy might have the same outcome.

I think you’re forgetting the fact that the founding fathers were revolutionaries. They very obviously felt the need for the people to have the tools to depose a government if necessary. However, they did not foresee the US becoming a superpower, or the extent to which weapons technology has progressed.