True, but does the law against it stop any that want a firearm from having one? Besides even convicted felons are subject to the predation of other criminals, whether they have gone straight or not. It is immoral to remove such protections as they have in prison, while denying them the means to protect themselves.
All that Law does is give the Legal System another tool to put people away a little longer, once they re-offend. There aren't a lot of people in Society that are willing to hire ex-cons. It is almost inevitable that most of them will commit new crimes.
As for the morality of denying firearms to felons I guess that's a matter of opinion. Personally, I feel that all we'd really be doing is arming them to commit new crimes. There have to be consequences for those who choose to break the Law.