It seems to me the principle of Res Judicata is a rather fundamental doctrine of most governments in the world where incarceration and punishment is not allowed to become a tool of repression by the government, and particularly bearing on the suppression of those in opposition to said government. The danger in weakening such a fundamental principle is the loss of protection for all of us, even when additional proof comes to light.
In the same way Freedom of Speech allows a Ku Klux Klansman to rail against blacks, Jews and immigrants, it allows those in diametric philosophical opposition to the Klansman to question the unrestricted and illegal use of power by the government.
We should never celebrate the fundamental erosion of an important right in the name of a short term and specific satisfactory result without considering the long term implications.