When meat eaters tell you it's natural for humans to eat meat, remind them that modern man has been around 70,000 years and industrial farming only 100. The way humans get their meat now is nowhere near natural. 100 years ago, most people were close to the animals. They saw slaughter first hand. Today, they are oblivious to how meat gets to their plate. 100 years ago animals lived normal lives before they where slaughtered. Now, from the minute they are born, they only live a nightmare.
The attitude meat eaters have today towards animals is very similar to how plantation owners in the southern U.S. treated slaves- They are just beasts, no need to care about their mental and physical pain and suffering.