I yam sorry, Mr. berger, but the constitution is very explicit.
When you start saying, "just because that's what they said, it's not what they meant." You might as well be a flaming liberal or a socialist.
I'm going to assume that you are using the term "liberal" in a pejorative sense. You see, our form of government is a "liberal democracy." And "socialism" is more interested in economic outcomes than civil libertarian ones.
So, name calling aside, our Constitution didn't rise up from nothing. It was predated by centuries of political thought. Jefferson didn't come up with the Declaration of Independence by himself. The words:
We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness. --That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed, ...
are products of political treatises by St. Augustine, Thomas Hobbes, John Locke and John Calvin to name a few.
The founders were WAY smarter and more learned than me. Or of You.
It is tempting to hold up the founders as gods to be worshipped, but they had faults, too. Jefferson ended up in a huge fight with the Supreme Court over the power of the executive branch. He thought that since he was president, he was beyond reproach. (MArbury v. Madison) He was wrong. The founders were men, great men that created the greatest form of government in the history of man, but men and fallible men at that.
And yes, "they had felons in yon days of yore" and they were treated as pariahs and undeserving of the benefits of citizenship.
Having exhibited a propensity to violate the social contract on at least one previous occasion, criminals cannot be trusted to exercise the franchise without corruption. Allowing ex-convicts to retain all of their rights of citizenship could have a perverse effect on the ability of law abiding citizens to reduce the deadly and debilitating crime in their communities.
A variant of this argument focuses on macro-level consequences for the legitimacy of democratic government. It maintains that the purity of civil rights are undermined by the participation of tainted individuals. In the philosophical arguments associated with the republican (small r) and communitarian traditions, for example, the political community can remain viable only insofar as it consists of citizens who respect the rules of democratic procedure and can be expected to live within the norms those rules generate. In conservative variants of these arguments, the presence of criminals within the polity potentially erodes confidence in the community by diluting the rights of noncriminal citizens.