The Egg doesn't have to be protected, the monkeys inside the Dome have to prove that they are capable of protecting the egg.
Like how high school kids pretend that a sack of flour is a baby.
Everything is about establishing that these apes have character and decency in preparation for what is to come...
How decent is it to force children to kill Big Jim?
Double standard much, or is this a test to see if the kids will stand up to power?