Also why disarm him after he has served the public for many years making him an easier target for payback from the felons he protected us from ?
For the same reason you would disarm the rest of the law abiding US citizens that also deserve to be able to protect themselves just as much against the felons who will pray on them even more so than on the police.
It's a bad idea no matter who you apply it too. And I have to agree with delarosadavid, you can't make a special class that gets to keep guns while the rest are prohibited. That is simply discrimination.