I agree with everyone that under ideal conditions, with excellent shot placement, lighter rifles do the job. A headshot with a .223 is going to work on deer, isn't it?
Now, what about the not so ideal shots? That 12 point buck who got that way by showing nothing but tail everytime it hears, or sees, a hunter? All you have is a texas heart shot, and, you want something that will penetrate full length deer, and create enough of a wound channel to put the deer to rest quickly. I think the mags get a bad rap, since they use light bullets, that explode, or, due to high velocity, fail to penetrate. If used with a heavier bullet, you can get both expansion, and penetration, at a much large caliber size. Hawk bullets are a good example of a bonded, heavy hollow point, that can be tailored to what ever rifle, and velocity you want, since they make different thickness jackets. I think the mags give you the chance to get good velocity, with heavy bullets, that expand, and penetrate well. My topic would have been people using bullets that don't penetrate sufficently for their target, regardless of caliber. In other words, you get caught with a soft, when you need something that's heavier, and penetrates better for the shot you are taking.
I have noticed a trend here to think shot placement is everything, and, that negates that hunting doesn't occur in a perfect world.