Will a .357 magnum kill a deer? Sure it will.
Will a .223 kill a deer? Sure it will.
Each cartridge within its limitations and more importantly, within the limitations of the shooter, are adequate for whitetail deer. Not optimal, but certainly adequate.
A young friend of mine, a junior high-schooler, recently took her first deer with a .357 magnum Marlin lever rifle. She and her dad were hunting in a swamp forest in Louisiana. Swamp forests here are generally typified by mature trees with an understory of brush and palmetto and ranges are generally limited to 100 yards or less. Here, I'll let her dad tell you about it.
I think Rachel feels a .357 carbine is adequate for whitetail deer hunting, under 100 yds. Dec 27, Tuesday morning, she killed a 2.5 yr old 7 pt buck, live weight of 150 lbs. It is her first buck, and the first one I actually called in by grunting. We saw it grunting and chasing a doe thru the palmetto bushes, and when I grunted, the doe turned on her afterburners and left while the buck stopped and started looking for the "intruder". I grunted one more time, and the buck started easing our direction thru the brush. When he got within 40 yds, he slipped out onto the trail to get a better look, and my daughter was ready. Deer was quartering towards us, bullet hit forward on the on-side shoulder, penetrating diagonally thru the right lung, liver, stomach, and ended up just in the muscle in the upper part of the left hind quarter. Yes, nearly 3 ft of penetration from a factory Remington .357 Mag 158 gr soft-point load. I recovered the bullet when we were deboning the meat to grind.
I'd say that almost 3 feet of penetration from a factory soft-point .357 is adequate for the task at hand.