Honestly a more reasonable moral approach would be to try to quarantine and cure the plague with the help of Uther's paladins.
That would ideally be my option, but it's difficult to tell how viable it is. The First and Second Wars against the Horde devastated humanity. Even if we assume there was a baby boom after the Horde's defeat, it has only been 10 years since the Orcs were interned, not enough time for a new wave of kids to be old enough to be used as competent soldiers. I am not sure if Arthas could muster enough soldiers from local garrisons to surround a "city" and prevent the spread in time.
On a related note, I find it funny how Shadowlands' narrative says that Uther did wrong by treating Arthas as evil, after having murdered his father and destroyed his kingdom.