When God created the world, He did not permit Adam and Eve to eat meat:
And God said, Behold I have given you every herb bearing seed, which is upon the face of all earth and every tree in which is the fruit of a tree…to you it shall be for food. And to every beast of the earth and to every fowl of the air…I have given every green herb for food. (Breisheet 1:29-30)
In 1:28 God gave the blessing to be fruitful and multiply and “have dominion over the fish of the sea and over the fowl of the air, and over every living thing that crawls upon the earth.”
Humans were told to have dominion over the animals but not to slaughter them or eat them.
After the flood and the immoral behavior that led up to it, the focus was on man refraining from killing other people and respecting human life. Man was no longer on the high moral level that would require him to forego the slaying of animals.
According to Rav Avraham Yitzchak HaKohen Kook, the “heter” (dispensation) to eat meat is only temporary. When the time is ripe, the latent aspiration for justice for the animal kingdom will come out into the open.
In the desert, the only red meat that was permitted was meat that was part of a sacrifice in the Mishkan (Tabernacle). Once they arrived in the Land of Israel they were permitted to eat meat as long as it was slaughtered properly.
Rav Kook points out that the path of following the laws of kosher slaughter will eventually lead us back to abstaining from eating meat.
Nehama Leibowitz deduces that once we fulfill Yishayahu’s prophecy (which is well know from the famous Israeli folk song) of “Lo yisa goy el goy cherev, lo yilmedu od milchama”, “Nation shall not lift up sword against nation, neither shall they learn the arts of war anymore”, once humans stop killing each other, then we can expand man’s compassion to the animal kingdom.
In the mean time, for those who do eat meat, it should be slaughtered and eaten in a respectful manner. There are a lot of disturbing phenomena in the Jewish community concerning meat and the treatment of animals: Some slaughterhouses are Halachically kosher but the animals are not treated properly. It is unacceptable to have chickens cooped up all day in horrible conditions waiting for Kapparot to be performed on them. Overindulging on meat at “all you can eat” buffets may be kosher, but not in the spirit of the law. A solution must be found for the amount of meat that gets wasted at weddings. Ostentatious siyum parties (which celebrate the completion of a tractate of the Talmud) at restaurants during the nine days leading up to Tisha B’Av make a mockery of the idea of refraining from meat and wine as a symbol of mourning for the destruction of Jerusalem.
We have not reached the point where we are on a high enough spiritual level for the entire Jewish community to be required to return to vegetarianism. However, even those who do eat meat must show respect for all creatures.