The two issues are separate.
/johnny
Felons know that before committing the crimes and it is a choice they make. If caught and convicted there should be negative consequences to their lives.
Many if not most felons do not commit just one felony but continue on the path of criminality.
This law does not stop the convicted felon from getting a gun. This guy did and he stopped the bad guy. Now he has face the consequences of the free choice that he made. If he is a good guy that made one mistake a long time ago then charges may be dropped or he may find a sympathetic judge or jury.
He also had the option of applying to the governor for restoration of rights. As I said before AFAIK felons are allowed to own black powder weapons so his right to defend himself with a firearm hasn't been taken away.
I agree with you that it is immoral but I think the two issues are intertwined. Using a law as a band-aid for another undesirable aspect of government, you make it that much harder to fix the original problem. Eagles6 sees a problem with lenient sentensing. By creating laws addressing the ill affects of letting criminals out early we are now enshrining the poor sentensing practices and making them harder to fix.