Walkers are dangerous but Hershel doesn't know he have lived outside that world. Even if they are considered humans gone crazy people they really aren't like Jenner said about the part of the brain that makes you human is dead. Shane had gone mad and now is being honest with what he think. He wants to protect the ones he care for but by the incorrect means. You could debate that in that era there isn't incorrect means. And so he free up the walkers instead of killing them upside and rejects everything the hoster thinks. Only taking action, the world of the strongest. Sophia appears but now as a walker, neglecting all effort Daryl put into saving the girl.
Review of Pretty Much Dead Already
