Good question. I think they simply utilized common sense; one thing the Founders understood well was human nature, along with its potential for abuse. They were careful to protect the rights of the individual from the government - in large part because they correctly realized that those rights are God-given and inalienable, not government-granted and subject to revocation.
While this was later, another thing that probably played a role was the French Revolution. Some of the Founders, such as Jefferson, initially thought it was a wonderful idea, but Adams had it pegged from the beginning. While it was considered a step toward democracy, and it predictably disintegrated into a dark and bloody period in history.
I know that Jefferson, Paine, and to a certain extent Benjamin Franklin (at least, the site The American Catholic indicated he initially liked the French Revolution) definitely supported it. However, I’m not entirely sure Jefferson and Paine were really naïve about what it was about.
For starters, unlike the other founding fathers who at least had the excuse of being separated by the Atlantic Ocean and had fairly slow communication, Jefferson was actually there as the French Revolution was going on, even witnessed Bastille Day first hand. He knew exactly what was going on, yet not only supported it, but even helped draft the Declaration of The Rights of Man and the Citizen (as a matter of fact, his stay in France as ambassador is EXACTLY why Jefferson was not involved in the Constitution). If he had his way, I wouldn’t be surprised if we had something similar to France. And get this, he continued to support its excesses up to and including the events of the Reign of Terror, to the extent that he even denounced William Short when he tried to inform him what was truly going on (and Short was like a son to him).
And as far as Paine, his Age of Reason book published after the events in France indicated he did NOT learn his lesson about the French Revolution, especially regarding atheism.
In fact, probably the only one of the three who actually DID learn their lesson was Benjamin Franklin due to his coining the wolf and sheep supper analogy denouncing democracy at least.