As a really avid 9mm shooter and bowhunter, I have to agree with what these guys are telling you. The 9 is a good round for varmint and small game hunting out of an accurate pistol, like my 92FS. However, it just doesn't carry the bullet mass and velocity needed to humanely kill deer. Yes, it does carry loads more energy than an arrow, but as these folks have said, an arrow kills in a completely different way than does a bullet.
It's my belief that an arrow through the lung/heart area that doesn't hit any bone is the most humane death possible when hunting. Think about it. If you've ever cut yourself with a really sharp knife, you'll notice it doesn't hurt, but man it bleeds. That arrow goes through those organs and cuts them cleanly with little drag and almost no shock. It simply passes through and sticks in the ground on the other side. Deer hit with this usually do not know what is going on. I've seen many of them run a few feet and stop to look around, wondering what is happening. Then they pass out and that is it.
A bullet hits and it immediatly transmits shock; the more the better. It destroys bone and tissue and does some bad things once inside. Some bullets, like most high-powered rifle bullets, are designed specifically to penetrate deeply and expand in a controlled fashion. Others, like varmint rounds and most rounds for the 9mm, expand very quickly, but don't penetrate very deeply. The 9mm will expand quickly, but since it still doesn't have nearly the speed of a heavy varmint round, like say a .243 (which I think is a little light for deer) with the same sized bullet, it just isn't adequate. I've hunted deer with a .357 revolver, and it is adequate under ideal conditions, but I would probably opt for something larger still. Hope this helps.