OK, so ignoring everything about the American Constitution (I'm British, we don't give a toss about you colonials), and on the topic of trustees v. delegates, why not have both?

As has been pointed out, there are positives and negatives to trustees (act in best interests, undemocratic) and delegates (democratic, not necessarily wise). One way around this is to employ both.

One of the very good ideas contained within the US Constitution is the principle of checks and balances. It's pretty obvious that trustees are the more capable rulers; the problem is when they don't act in accordance with the will of the people. So stick in a second house (of a bicameral system), and give them the power of veto.
Alternatively, if you lean more towards democratic but potentially flawed delegate rule, establish a second house made up of trustees and give them the power to veto any really stupid ideas.

The most capable rulers are the people.
This simple truth escapes so many subjects of monarchs.

That's simply not true.

There are people in my country who go out and vote for the BNP, a neo-Nazi organisation. These people are not fit to govern as individuals, and they are not fit to have their opinions recognised as part of a collective decision. On a national level, and on a parliamentary constituency level, they haven't won any power. But in certain localities, they've been elected as councillors.

Let me repeat that. In democratic elections in some areas, members of a fascist organisation have been chosen by the people. The people are - or at least have the potential to be- *extremely fucking stupid*. They are not the most capable rulers.

That said, the people also have the right to sovereignty, and it's even easier for an individual to be extremely stupid than it is for a mass of people, especially when an effectively random system is employed for selecting an individual ruler, like the circumstances of birth.

http://newsone.com/nation/casey-gane-mccalla/ron-paul-made-south-was-right-civil-war-speech-with-confederate-flag/

I can see who you will be voting for, \r.

http://newsone.com/nation/casey-gane-mccalla/ron-paul-was-implicated-in-attempted-white-supremacist-island-invasion/

Trustees all the way!

So fascism isn't in human nature.
All you helpless fools who think a small group can do better than the masses sicken me with your ignorance.
Post when your intellect matures Worldbeing.

Athens reached its Golden Age under radical democracy.
Rome was infinitely superior under the Republic than the Empire.
The United States took government and power to heights the corrupt British monarchy couldn't even dream of.

Yes, the people are infinitely superior as a vessel of government power.