Let me start with full disclosure. I sleep with my dog and have always slept with my dogs, with the exception of my dog Lucky, who unaccountably preferred to sleep in the bathtub.
Aside from my personal preference, as a veterinary behaviorist, I can say that there is no reason why most dogs should not sleep in their owners’ beds if they and their owners prefer the arrangement. Dogs are social animals and enjoy the comfort and feeling of safety that sleeping near members of their social group confers.
Dogs can certainly get used to sleeping in other areas of the house i.e. in a crate, in a dog bed, etc. if the people they live with don’t enjoy sharing a bed with them. There are many reasons that people may not want a dog in their bed – dirt, hair, snoring, etc. and that is entirely reasonable. There are also many reasons why the dog may not want to sleep with its owner. She may not enjoy the owner’s snoring, the bed may be too hot or too crowded, etc.
There is a lot of talk in the popular media about how it is important for dogs not to sleep in the owners’ beds lest the hapless owners find themselves dominated by their dogs and relegated to the bottom of the pack, and find that obedience and good behavior have gone out the window. Some owners are even shamed in the media for sleeping with their dogs. These views derive from the mistaken notion that dogs, like wolves, have dominance hierarchies that in the case of dogs, include humans. And using the argument about dominance, proponents say that letting the dogs sleep in such a high-value place (or eat first or walk ahead of the owner or initiate play with the owner, etc.) will cause the dog to think that he is dominant over the owner, which will lead to the horror of being submissive and thus at the beck and call of the dog.
The dominance idea comes from studies of captive wolf behavior by David Mech, which has since been debunked. Even wolves are no longer thought to behave as was once believed. https://sciencenorway.no/ulv/wolf-packs-dont-actually-have-alpha-males-and-alpha-females-the-idea-is-based-on-a-misunderstanding/1850514 Furthermore, the new data on dogs show that dogs are behaviorally very distinct from wolves. Dogs live in loose, flexible social groups. They are attached to us but do not think of us like dogs. They do not have pack leaders among themselves and do not think of us as pack leaders. Thus the notion that dogs spend their lives trying to seize the alpha position and push us down in the hierarchy (therefore requiring us to be vigilant about keeping them in their places) is incorrect.
Dogs do not need to be dominated. What they need is understanding of their needs and body language as well as structure, consistency, and predictability. Like all living beings, they do best when they feel like they can predict and control what happens to them. They like to know that their actions can have predictable results (like when they follow a cue such as “come” they get a reward). Most of what is thought to be stubbornness, disrespect, or refusal to do what we want has been shown to be lack of understanding of what we are asking of them and lack of a clear, predictable, and consistent consequence. In addition to lack of clarity, dogs sometimes receive mixed messages. People may accidentally reward certain behaviors they are trying to discourage – like petting a dog that jumps up and yelling at them to get down. And sometimes, when people use force with the dog, she does not obey because she is too anxious or in a state of learned helplessness.
What does this have to do with sleeping with your dog? Just this. If people want to sleep with their dogs, they should make a decision about it and be consistent. There are many reasonable options. They can choose to let the dog on the bed. They can choose to let the dog on the bed some of the time (i.e. for morning cuddles). They can choose to allow the dog on the bed by invitation only. Or they can choose not to have the dog on the bed at all. They just need to be consistent and clear with the dog about the arrangement and the dog will settle into the expected place.
Another argument that is used against letting dogs sleep in bed with owners is that it spoils them, which makes them more likely to misbehave/be disobedient. It turns out that a study found the opposite. Spoiling activities like sleeping with the dog and feeding the dog “people food” have no detrimental effects on obedience or behavior.
There are certain dogs and certain situations in which it would be ill-advised for dog owners to sleep with the dog.
Puppies should be in a safe enclosure (crate or pen) when they cannot be supervised. I learned this the hard way. When I was young I slept with my puppy and woke up to find she had chewed a large chunk of my long hair off.
Irritable or aggressive dogs
Dogs that have a history of growling or biting when disturbed while resting and dogs that may guard the bed from the owners or other animals should not sleep in the bed. It is not safe. If there are young children in the home, dogs with these issues should sleep in a place where no one will disturb them at night, like a crate, pen, or behind a gate.
Co-sleeping with infants
Dogs should not be on the bed when infants are sleeping in or near the bed and in a co-sleeper. There is a risk that the dog could accidentally suffocate or otherwise injure the sleeping infant if he slept too close.
Other human reasons
As I stated earlier, there are plenty of reasons why a person might not choose to sleep with the dog and they are entirely legitimate.
Dogs do not HAVE to sleep with people. But if you want to sleep with dogs, there is usually no reason why not. My dog agrees.