Many individuals who advocate for the humane treatment of animals in research facilities, abattoirs, or farms are often those who have a deep affection for animals and own pets. The majority of household pets, however, are rabbits and hamsters, and these animals are typically fed pellets that contain animal by-products. Consequently, many of those who advocate for humane treatment of animals inadvertently support such cruelty.

Which one of the following is an assumption made by the argument?