Better question: How can it be conscionable to continue punishing one after he has served his sentence?
By stripping one of their rights permanently you create a second class of citizens; moreover, the initial forbidding of firearms to felons is a violation of the Constitution's prohibition on Ex Post Facto law, even by the USSC's narrow view of what Ex Post Facto means (they deny that any civil law can be Ex Post Facto, asserting only that retroactively increasing criminal punishment qualifies.).
This seems like liberal activism masquerading as conservatism.
I don't think so.
I want to get on the record here, and your description of how this should be viewed is a good one, and one I agree with.