The second amendment does not exclude convicted felons. If the state thinks a criminal too evil then give the felon life or execute him. If the state says a felon has served their time…then the second amendment should apply to him as it does everyone else.
On one hand, you could look at it as a person is convicted of a crime (felony), does their time, and then is released. As the saying goes, they "paid their debt to society" for their actions. In that light, why wouldn't they be allowed to possess a firearm?
On the other hand, if losing your freedom temporarily (being incarcerated) is part of "paying your debt to society" why couldn't losing your right to possess a firearm (permanently) also be considered part of paying that debt?
Every once in a while I pull this issue out and think about it - but it doesn't keep me up at night.