I can see how it would work in a way. Obviously, the more you have the better off you are, if they were to heal up mark and let him go back to the group that would be less meat for them. Now over time, eventually the group would get mad and begin to worry about what is really going on with why Mark has not been seen. After all it was an arrow to the shoulder, not half his body being removed and put back together.
If they feed Mark to the group, perhaps they felt they could persuade them in a way, that "the meat wasnt so bad after all" and allow them to make the group understand sometimes it is for the best to kill and eat others.
Just my thought on it.