Animal cruelty? Causing disease? And general horrors? Another thing marx talked about (quote from Saito Karl Marx's Ecosocialism):

...Responding to...enthusiastic reports about the 'system of selection developed by English breeder Robert Bakewell, [in 1864] Marx wrote in his notebook: 'Characterized by precocity, in entirety sickliness, want of bones, a lot of development of fat and flesh etc. All these are artificial produces. Disgusting!'