There are numerous reasons to keep pet rabbits indoors. Anyone can visit www.rabbit.org (House Rabbit Society) for more information, but I listed a few reasons below. If any of you wish to know more, please, feel free to contact me. I am a license HRS Educator and I also founded and am director of a rabbit and small mammal rescue in Arizona called Rascally Rabbit Rescue and Critter Haven of Arizona, Inc.

Reasons to keep rabbits indoors
--Predators: no one wants their pet to "disappear" one day because s/he is lunch for hawks, owls, coyotes, cats, dogs, etc.
--Heat: rabbits should never be in temperatures above 80 degrees for more than a couple minutes. The heat makes them more susceptible to disease, as the stress compromises their immune system, and rabbits easily suffer from heat stroke and die at any temperature above 80 degrees. This is the same for chinchillas and guinea pigs.
--Cold: this one is more obvious, as it is easy to freeze, even with a beautiful fur coat. Rabbits need a way to stay warm in temperatures below 55 degrees.
--Viruses: wild rabbits, like cottontails, carry viruses that can also infect domesticated rabbits. These viruses are deadly and an infected rabbit usually dies within 14 days (sometimes a lot less depending upon the virus).
--Flystrike: flies lay eggs in damp areas, including a rabbit's litter box, and the larvae can easily access the rabbit, burrowing under the skin and causing damage. The damage varies depending upon where the flies burrow, but it can lead to unexpected and sudden death.
--Bot flies: nasty little parasites hang out just under a rabbit's skin. If you've ever seen one, you wish you hadn't, and if you haven't hope you never do.
--Neglect: Out of site=out of mind. How many people go outside daily for an hour or so to spend time with their outdoor pets? Not very many. Rabbits don't show that they're ill until they're very close to death (as in, they die the next day). Unless you're around your rabbit regularly, you won't notice the very subtle differences in behavior when your rabbit is ill or injured. All prey animals hide their pain and illness so as to not appear weak to predators. Unfortunately, this means that they hide their pain and illness from their human companions far better than a dog or cat.

If you have questions or if you want to learn more about these wonderful pets, please visit www.rabbit.org.

Thanks to both who responded with answers.