Crating a dog overnight is actually a good practice and isn't cruel. A dog that's crated overnight won't get aggressive. Domesticated dogs have the same instincts as their wolf ancestors and want a den of their own. Crate training should be a part of training for puppies and older dogs. Here are the general rules for crating a dog:
1. Crating a dog overnight is fine as long as the dog has had sufficient out-of-crate time during the day.
2. Dogs are social animals and need the companionship of their families and other animals. Your dog should never be crated for longer than eight hours, at the most.
3. Older dogs and puppies need more time out-of-the-crate for potty breaks. You should make sure they go out at night before being crated.
4. A crate should never be used as a form of punishment.
5. With proper training your dog will see its crate as a safe haven.