Kain does argue at first, but then he sees the sense in it. "Remember, we must avoid drawing any attention to us." That means they have to leave when the time comes to leave, with or without any freed prisoners. Not that Kain is against trying to help people... but they have to be realistic here.

At first, it seems to be going well enough, they manage to get close enough to finally find where they're holding the captives... Good, this should give them some insight.