The Constitution did originally call for a weak government and I believe our government is way too powerful. As a libertarian, I don't believe the government has any right to impose on social issues such as drugs, prostitution, gambling, and gay marriage. Even state governments I don't believe should have this right. Income tax used to be illegal, but the federal government instituted it as a temporary wartime measure. Look at where we are now.
While I believe the government needs some power...I don't believe it should be as powerful as it is.
It has it's power due to the ignorance of the people....I don't believe it is any flaw in the docements. The documents called for changes to be made as needed (i think so anyway, i don't feel like looking them up at the moment) and at the time, we don't need this strong of a government.