"Removing mild, survivable challenges from the environment could thus leave the immune system less 'tuned' for the full spectrum of challenges it faces" Exactl

"Removing mild, survivable challenges from the environment could thus leave the immune system less 'tuned' for the full spectrum of challenges it faces" Exactly. You want to protect people from, say, Rubella ... but I think we should proceed with caution with things like the cold and the flu ...