Humans have intelligence and are able to reason like no other animal. We do not rely on insticts any more and have no real need to harm other animal. With that it is cruel to eat meat and grow live stock just to slaughter and eat them. We can get all of our nutrients by other means and have no use in meat.
I definitely think that there are some ethical problems to eating meat. While I do not see a problem with it, some people do. I think that a lot of the arguments against having meat in a diet is that it is no longer necessary to eat meat for protein since a lot of foods have it.
It is natural though, mankind would not have evolved this far if we never ate meat. The protein in meat is very good for our brains. While I would not recommend eating your own dog. We can raise certain animals and treat them humanly to feed us are required meat.
A balanced diet is very important, and that means both meat and plants. There are humane ways to raise and kill animals for eating. In general it is absolutely fine. The human body is designed to digest it and runs better with meat than it does on just fruit and vegetables.
The world is set up in a way where we take what we need from our surroundings. Animals just so happen to be part of those surroundings. Meat taste amazing and is a very good source of calories when needed. Animals kill for food and humans are just glorified animals.