Maybe Herschel isn't such a d-bag. If he true-ly believes that they can be helped, maybe Herschel hid the girl from the group because he knows the group kills zombies. That means he could be saving her life by keeping her secret(in his mind).
Also, in his own way he was trying to get them to give up the search by constantly telling them to leave.
I think all this gives Herschel more depth than he had in the comics.