What we call oligarchy now and what they called democracy then -- it's the same picture. Re democracy's weaknesses, I think the most important factor was that

What we call oligarchy now and what they called democracy then -- it's the same picture. Re democracy's weaknesses, I think the most important factor was that whatever their radical ideas, they were living in a country that had been born out of a revolution / civil war and were living through the failure of one attempt at creating a country (the Articles of Confederation) so they were primarily concerned with creating a system that could actually work for a while and maintain stability through turbulent times. They were true believers in (what they called) democracy, enough to bet the future of the country on it, but they also believed it had weaknesses, and they did not want to embarrass and discredit it by building a democracy that failed because of something that seemed inherent to democracy itself. That's one reason they were obsessed with its weaknesses. Another other reason is that they had to sell their new system to democracy skeptics. So, they had to convince both themselves and others that their system built around the idea of democracy was designed in a way that guarded against its weaknesses.