We are talking about a super rabies virus that totally wipes out the "personality" part of the brain, making the person equivalent to them being dead, except that they are bloodthirsty monsters now.
By "dead" we mean all traces of the old person's thoughts, emotions, and memories have been destroyed.
Except they aren't dead. They are alive. If they are alive there is a chance we can cure them. We must find out whether the wipe is impossible to reverse. If it isn't then we'd have to euthanize them, if it is reversible we'd have to reverse it. If we don't know/can't find out we'd just have to contain them.
So when we are attacked by another country should we figure out what is wrong with them and try to help them get past their stage of wanting to kill us? People that are trying to kill other people lose their rights. When you pull a gun on a cop you officially forfeit your right to live. Same would apply to becoming a zombie.
But its not their fault. Yes, if they are going to kill you and there really isn't a way around it shoot them. Yes, during the inital outbreak of panic blow their brains out. But after that, when stability has more-or-less returned (because a zombie apocalypse would never actually destroy civilization) then we need to start trying to make them better.
I'm not saying don't kill zombies if you have to. I'm saying when you don't, you shouldn't.
If a mentally handicapped person grabs a gun and starts shooting it doesn't matter whether they can help it or not, they are shot.
I don't see this magical point of "after the panic" that you are talking about. Do you mean the zombies will come down and chill? Or we should get used to them and let them eat us? There's no safe way to catch a rabid person with a disease spread through bodily fluids.
Another point, brain dead people don't ever gain their cognitive functions back. Once a zombie permanently a zombie, the non zombie parts of the brain are shut down and killed by the virus while the instructions for being a zombie are left functioning. The person is completely gone and will never return.