They believed in liberty, defined as the freedom to do good.
No, they didn't. They quite clearly believed that liberty was the right to do as you will, as long as you do not impinge on the rights of others. Read the second Jefferson quote I supplied.
They never believed that anyone had the right to do wrong.
It depends on what you mean by wrong. Whose definition of wrong? What context of wrong? Jefferson explicitly defines wrong as impinging on the equal rights of others. If you want to define wrong within the confines of Judeo-Christian morality, I can provide you pages of quotes from the founders that expound on the dangers of a national government that imposes such a morality on its members.
Modern libertarians don't believe in liberty, rightly defined. They believe in licence.
That is, of course, completely untrue, mostly because it is a gross generalization. But we weren't talking about modern libertarians. We were talking about the founders, so your statement is without meaning to the discussion.
It always comes down to that, doesn't it.
The founding generation had a shared knowledge of what right and wrong are, based in a shared theology and worldview.
Also, folks have consciences that speak to this question. Even little children have an intrinsic knowledge of the difference between right and wrong.
The fact you even have to ask the question speaks volumes, frankly, and goes to the reasons the country is as screwed up as it is.
Thomas Paine:
"Those who expect to reap the blessings of freedom must, like men, undergo the fatigue of supporting it."
"Tyranny, like hell, is not easily conquered; yet we have this consolation with us, that the harder the conflict, the more glorious the triumph.
"What we obtain too cheaply, we esteem too lightly; 'tis dearness only that gives everything its value. Heaven knows how to put a price upon its goods; and it would be strange indeed if so celestial an article as freedom should not be highly rated.
"The cause of America is in a great measure the cause of all mankind. Where, some say, is the king of America? I'll tell you, friend, He reigns above.
"Yet that we may not appear to be defective even in earthly honors, let a day be solemnly set apart for proclaiming the charter; let it be placed on the divine law, the Word of God; let a crown be placed thereon.
"The Almighty implanted in us these inextinguishable feelings for good and wise purposes. They are the guardians of His image in our heart. They distinguish us from the herd of common animals."
"I would give worlds, if I had them, if The Age of Reason had never been published. O Lord, help! Stay with me! It is hell to be left alone."
"I die in perfect composure and resignation to the will of my Creator, God."