No matter how good the Kingdom's anti-undead security measures were, they couldn't distinguish the regular living from those in the process of being turned into undead.
Not even Life Vision could do it. Even Awakened would need to examine everyone present with Invigoration to recognize them and even if they did, many thralls didn't even have a blood core since their master belonged to an undead species that couldn't bestow upon them any power until they were turned.
Only Soul Vision allowed a Guardian to identify from a distance the presence of a pseudo blood core or the deep-seated despise for the living typical of those who choose to become an undead.
Most of them were power-hungry people willing to pay undeath's heavy price, but some of them were just people suffering so much that they would do anything to make the pain stop.
