As we've discussed here, crate-training your puppy should be one of his first obedience lessons. It lays the foundation for more advanced training, it aids greatly in house-breaking and it just plain keeps him safer when you aren't around. It's not mean—it's the right thing to do.
More recently I came across a blog post on the subject by professional retriever trainer Rick Grant on the SportDOG Brand website. It's well worth the full read, as it delves into four hunting-dog specific reasons to crate-train your dog.
My favorite point Grant makes is one I had not considered: One day you'll have to send your duck dog ahead of you for retrieves or your upland dog—be it a pointer or flusher—ahead of you to hunt.
"With those concepts in mind, what better way to reinforce the concept than sending [your dog] to his kennel?" Grant writes. "Once your dog knows what 'Kennel' means, you should be able to send him there from 10 feet, 30 feet, or really almost any distance."