Just a couple plot questions... [spoilers]

[Sexbad]

Spoiler below!

I'm certain that Clarence is a sort of deformed child of the Tuurngait. All the other infected duded are connected to he hive mind. Before Clarence was cast into Phillip's body, he was part of the Tuurngait mind. He recalls Red calling "us" a disease. If Red was left with an alone twin of Clarence, the hive mind would not recall that.

The hive mind believes that the needs of the many are greater than the needs of the few or the one. They most likely left him to die in there because one extra infected wouldn't prove much use in the siege of the mines and the Shelter.