Whether we look at modern Jewish social justice work or ancient rabbinic rulings, Jews have always insisted on the importance of having compassion for animals and reducing unnecessary animal suffering—tsa'ar ba'alei chayim in Hebrew.
Put most simply, when I choose not to eat meat, I feel that I am choosing life over death.… –Jonathan Safran Foer, author of Everything is Illuminated, winner of the National Jewish Book Award
Increasingly, this fundamental reverence for life has led Jewish leaders to advocate vegetarianism. From the first chief rabbi of pre-state Israel, Rav Abraham Isaac Kook, to giants of Jewish culture such as Albert Einstein and Nobel Prize for literature winner Isaac Bashevis Singer, the vegetarian diet first prescribed in the Garden of Eden (Genesis 1:28-29) has been held forth as "a kashrut [dietary law] for our age."
We can all agree that animals should be treated humanely. Today's kosher meat comes from the same abusive factory farms as all other meat. Despite the humane intention and spirit of the Jewish dietary laws, there are no standards to ensure that kosher slaughter is any less cruel than conventional slaughter. In some instances, it's been shown to be much worse.
In the face of horrifically cruel and ecologically devastating factory farms and a kosher industry that has sanctioned even the most grisly abuse of animals, it's difficult to see how eating animals is compatible with Jewish values.
The following are examples of the cruelty and suffering that animals endure in the food industry.
Additional information about Judaism and vegetarianism can be found here.