Let's discuss this from a professional veterinary perspective:

1. Cats don't dirty the bed; the bed dirties the cat. Kittens have a strong self-cleaning ability; they lick their fur for 2-3 hours a day, equivalent to a human taking 20 baths. Cats' mouths contain lysozyme, which not only removes odors but also kills some bacteria. The biggest difference between them and humans is their cleanliness. They will lick their fur for a long time after you pet them or after eating, not to mention when you hug them. If you don't bathe them regularly, they will get dirty.

2. Cats sleeping on the bed might worsen a kitten's sleep quality. Humans and cats sleep well because the purring they make stimulates dopamine release, making us feel happy and relaxed. However, for cats, if we sleep too soundly, we might squeeze or wake them up. While we relax, we disturb their sleep.

3. After a cat starts sleeping on the bed with you, it will become increasingly clingy. Cats are naturally solitary and aloof, and not overly dependent on humans, unlike dogs which wag their tails at everyone. Most cats are quite reserved and difficult to move, but once they start sleeping on the bed with you and become familiar with your scent, they can easily transform from a cool, aloof cat into a devoted puppy. They won't want to leave you after sleeping together, and will definitely lie on your lap or at your feet whenever you're nearby. This is because they've been used to being close to you since they were kittens. Before sleeping on the bed, they might sometimes ignore you even when you offer treats, but after sleeping together, they'll rub against you for ages whenever they see you, completely shedding their previous aloofness.

4. As long as you regularly deworm your cat, kittens sleeping on the bed are generally beneficial. There might be some cat hair on the bed, but it's clean. Since kittens don't usually go outside, it's actually quite good for them.

A friend asked me what to do if their kitten isn't affectionate? The best answer is to let them sleep on the bed with you from a young age. This way, they'll become familiar with your scent and build a strong bond. (They're all warm and cozy in winter.) Kittens usually see their owners as brothers, sisters, or even partners, but they generally don't see you as their master, haha, they don't have that concept.

5. A healthy kitten won't have bad breath or body odor. If you notice it, it's usually because of tartar or plaque in its mouth. It's easy to check: just open its mouth and shine a Wood's lamp on it. Normally, it will be blue; if it's yellow, you've got it. Solution: For mild cases, I don't recommend teeth cleaning. You can give it a week of freeze-dried food with lysozyme and L-ascorbic acid for dental cleaning, and stop giving it wet food. Low lysozyme content can also cause bad breath. So choosing the right cat food is also very important. Cat food with lactoferrin and freeze-dried food, if you persist for a period of time, the kitten's condition is likely to improve. (When buying cat food, never buy the cheapest kind. You get what you pay for. Remember to check the ingredient list: it should be high in protein and moderate in fat. It's best to choose products from reputable manufacturers. Don't be tempted by cheap prices; very cheap cat food often uses inferior ingredients, with stale or very little meat, making it unpalatable to cats. Unscrupulous manufacturers may then add large amounts of chemical palatability enhancers, ultimately leading to malnutrition and poor health.)

6. Intestinal Problems: Weak small intestine digestion or a lack of beneficial bacteria in the large intestine often results in kittens with diarrhea and soft stools. (If they have diarrhea, they can't be on the bed!) The key to addressing this is using enzymatically digested fresh meat. This pre-digests the meat, improving absorption. Adding a little Saccharomyces boulardii can likely resolve these issues, allowing you to comfortably pet your cat on the bed. (Remember to deworm.)

Finally, one last point: Make sure your cat drinks enough water, otherwise they may experience urinary retention. This pet water fountain I use is great; I'm sharing it with you. Click to purchase if needed.

https://www.yezimo.com/products/smart-pet-water-fountain