People like pets that look cool or different. I used to sell one or two meat mutt rabbits from each litter as a pet, and it paid for the feed for the rest of the litter, making my freezer camp free. I just picked the "cutest" kits, let the kids handle the daylights out of them, and then posted their pics on craigslist under farm and garden. I emphasized that they were fun pets that were docile and well-handled, or edible, and that usually got them sold in a week. Over time I shifted my breeders more toward a particular breed, but as long as you are not misrepresenting your rabbits, I don't see anything wrong with selling the occaisional "pet" or cull.
It is true that production breeds are much more efficient than smaller "pet" breeds, but this is the difference between keeping a Rhode Island Red chicken flock vs. some Silkies or barnyard mix birds. Both will lay eggs. If you are happy with them then they are "useful", and learning on "mutts" is frequently better than investing in high end stock when you may discover that you hate breeding (or eating) rabbits and want to be done.
