amongst their own kind , though frequently copulating by carnal contact like the animals they were , faults were sterile , so the only reason why they still existed was their use as beasts of labour , for which purpose they continued to be bred , carefully so their population wouldnt get out of hand , with lurienites who had debased themselves such as deniers , or their mates and whose substance was deemed defiled and thus excluded from a proper surfacing rite .