Originally posted by That guy with the Spoon:

how does this make any sense? you invade a biome and it's inhabitants just let you pass through?
also what about leveling up skills? i wouldn't want less stuff to kill and loot for food or crafting resources.

Deer flee on sensing the character, do you do without deerskins? I bet not. They spawn, wander around, and run if they detect you

Low level mobs could do the same...they'd be far less annoying, yet still there in the world if you want to hunt them.