Probably the fact the modern meat, fish and dairy industry. It's an extremely inefficient system that contributes significantly to a whole bunch of major problems facing the environment: climate change, mass extinction and deforestation to name a few. It's responsible for unbelievable cruelty; many modern farming practices are morally indefensible. Furthermore, it's a serious blight on the human condition: it contributes to worldwide poverty due to the economics of mass-producing living creatures and it's a major source of disease due to the aforementioned farming conditions.

The humans of a thousand years will consider the animal farming industry as the very height of barbarism.