Human cruelty to animals is unjustified. Just because the practice is endemic it does not justify imprisoning animals within fences, walls or cages, for life. Neither does it vindicate the mistreatment of animals during their incarceration with the imposition of unnatural breeding, feeding and drugging practices, nor the untimely death sentences imposed.
Meat is not an essential food element for humans. Meat has never formed more than a mere supplement to our plant based diet. Currently less than half the world's population, of 7 billion, anticipate meat to be part of their diet, yet this requires the processing of 70 billion animals a year. This vast number takes up, by way of production and feed stocks, 75% of all farm land, equating to 45% of all land, 75% of all antibiotics produced, the consumption and contamination of the majority of all potable water, whilst causing the emission of over half of all human caused global warming gasses. It is now established by many scientists that a 25% reduction of livestock numbers would instantly return the world's atmosphere back to pre-Kyoto levels, would free up huge areas of land for the re-establishment of biodiversity of flora and fauna, as well as free up an abundance of grain and vegetables to feed every human being. It is not human who are a plague on the earth, it is the livestock being grown to feed them.
Meat eating is unhealthy. Studies in longevity all show an average healthy lifespan of vegans to be 10 years longer than meat eaters who are otherwise living in the same socioeconomic environment. It is no coincidence that the countries who lead the world in consumption of meat and milk, also lead the world in the incidents of cancers, heart disease and many other non-communicable diseases. The modern addiction to eating animal products is concurrent with the demands for pharmaceuticals simply to maintain a life expectancy similar to our ancestors who ate less meat, and took no medications.
The stool of logic stands, but the forces of market and emotion make it invisible to all but a few.