This argument is pretty old and there's some errors to it.

First of all, humans don't eat raw meat like carnivorous animals do so it's not really the same comparison.

Second, you should take a step back and look at things from a wider point of view. There's what, 6 Billion people on this planet. Most eat meat. You're telling me all of these people are wrong?

Third, you cannot survive off of only fruits, vegetables, and grain in certain climates. Try going to the desert, mountainous, or any other rough terrain and not consume any animal products. It just doesn't work that way, and man is too rational to make himself suffer and eventually die from not eating any animals in these areas.

It's a little easy to preach this message being in an area with a nice roof over your head and the ability to get a wide variety of food from the local supermarket or grocery store, but it's not like that everywhere in the world.