My main aversion to crating dogs is people who misunderstand the process and lock them up all day in the cage while they are off to work etc.. Crating can be a useful tool but dogs are not meant to be left crated for extended periods of time.
I came across this article that I really like:
Should you Crate your Dog by Suzanne Hetts and Daniel Estep, Ph.D
Crates, portable kennels and airline animal crates all refer to the small plastic or metal cages that are used to confine dogs or cats. There seems to be some confusion about how crates are best used. We will attempt to shed some light on this controversial subject by addressing some commonly held beliefs.
1. Crating a dog is inhumane.
Blanket generalizations such as this are difficult to defend. It certainly can be inhumane if a dog is confined in the crate for many hours a day. Dogs need exercise and as social animals, they need social contact with other animals or people. On the other hand, when a dog is sick or in danger of injuring herself, a crate may be useful and necessary. Also when a dog is properly acclimated and trained to the crate, it can be a humane and useful tool to keep the dog out of trouble or to transport her.
2. Since dogs are "den" animals, keeping them in crates is a natural thing to do.
Wolves, the ancestors of dogs and even feral dogs will sleep in burrows and other den-like areas, but they don’t spend their whole day there and they can come and go as they please. Many dogs can be trained to sleep in their crates and will go into them on their own to sleep, rest or just to get out of the way when things are too busy or stressful for them. The den idea should not be used as an excuse to isolate and confine the dog for prolonged periods of time.
3. Crating a dog is the best way to prevent or stop housesoiling or destructiveness.
It depends upon what is motivating the dog to housesoil or be destructive. If the cause is fear such as separation anxiety or fear of thunderstorms, crating can actually make the problem worse. For dogs that are destructive out of boredom or for other reasons, a crate may be appropriate. However there are other ways to confine a dog that may be just as effective, such as using a laundry room, kitchen or other doggy-proofed area of the house. Even in these cases, confinement by itself should not be the only step taken to address the problem. For example, bored animals should be given things to do to relieve the boredom.
In housebreaking puppies, crates are frequently used to take advantage of the puppy’s natural aversion to soiling where she sleeps. Here again there is a danger in overusing the crate. Puppies kept in the crate for very long periods may loose the inhibition to soiling in it and cannot be properly socialized to the family or other animals.
As with most other tools, crates are neither inherently good nor bad, it’s how they are used. After reading this review, it may appear to the reader that there are actually more negative consequences of human-companion animal interactions than positive ones. This is probably not the case. It was simply decided to emphasize the negative aspects that are too often neglected in other reviews of this research area. This was done to point out that negative consequences can result from human-animal interactions and that to thoroughly understand human-animal bonds, both the positive and negative consequences must be studied and evaluated.