OverextendedArgument is meant to stand in for the phrase An Argument can only go so far. Beyond a certain distance the Argument (point of view) becomes a liability and is counterproductive, as other considerations prevent a person carrying an argument all the way to solving the issue.
A case of AnArgumentTooFar. The opinion / explanation has stretched too thin and its use could become deceptive, if done on purpose.
We often see examples of these communication patterns when politicians start raving about.