Well you can consider it the only valid reason of course, but that's not to say that others are obliged to consider it that also.
The desire to be humane about it is a valid reason to "postpone the deaths" of animals and let them have a proper existence according to their natural behavioral repertoire. Not in small boxes being force fed to drag their unnaturally fat, mangled torsos chock full of antibiotics as fast as possible to the meat cleaver. Simply the desire to be humane is in itself a valid reason because we are human and in very much a real way we do not get the choice, less so in any case than we get to choose whether we eat meat or not. That's why we put so much effort in hiding the practices and most people - in Western societies at least - know meat only as pink packages of neatly cut shapes in cellophane with cooking instructions, you'll find in a cooler at the supermarket. You can eat yourself sick in meat without ever having to kill an animal or when living in cities even have ever seen a live one.
So while there are sides to the equation that are not so simple, a humane treatment of animals - letting them live their animal lives, letting them eat their own food (e.g. cows don't normally eat corn, they eat grass and preferably wild grass with herbs that they look for in relatively small herds) before killing them and live out our parasitic urges on their meat, seems not much more than just normal human behavior. We can of course look the other way, think of clever reasons why we should, but in hurting the animals we eat we are hurting ourselves and the results show.
I'm not very confident about it (reduction population, and a more sensible consumer behavior being more realizable than to increase animal well-being. It's a matter of meat being offered at ridiculously low competitive prices that won't allow for anything remotely resembling sensible farming and not even for a qualitatively good and healthy product. I'm convinced most farmers would very much like it differently and produce qualitatively good and healthy meat and treat their live stock right, but with the prices of today, it just not possible. And I don't agree that it's okay.
For me the only solution to a very wide range of problems is to drop the human population back down to about 1 billion and seriously curb our predilection to consumerism. There isn't much I can do about this though without becoming the most vile tyrant ever to rule the earth.
As long has hundreds of millions of people are heading to the market with coupons to save a buck a pound on food stuffs, the market will provide them with the most plausible response to their demands. The only way to do that is through high production processes that unfortunately detract greatly from the quality of the end goods, be they bushels of carrots, boxes of burgers, or plastic cups. To this end I praise those who shop at the organic markets but I reserve judgement of the majority who cannot afford such luxury.
Yes I think so it would be less strain on nature and environment
A lot of people here assume that the only reason for being a vegetarian is the "moral" aspect. As a vegetarian, and being close to many vegetarians, I can say that is not so. It is the disgust.
Its kinda like this: Some people don't mind eating cows and goats, but they find the idea of eating a dog or cat disgusting. They find the idea of eating human flesh even more disgusting. Which is irrational. To us vegetarians, we find ALL flesh disgusting. Its not the morality.