It's the waiting that's the worst bit, the hoping that they will come back as they are and not as something else, their eyes glowing silver blue and their head twisted by something else.
Most of the time they come back fine, they come back human, and everyone is just that little bit better off, with more food and supplies and medicine.
Other times not all of them come back, but none of them come back as Souls. They choose the other way out, the harder way out, to prevent themselves from betraying anything to the Seekers.
And their bodies don't come back either.