People don't know where those animals are going when they give/sell puppies and dogs on the side of the road. They just don't realize that it would be better to turn them over to Animal Conrol who will at least vaccinate, spay or neuter, and check into the backgrounds of the prospective homes. They often wind up as "bait dogs" for the cruel dog fighting rings. Sometimes they are sold to laboratories for experiments. Sometimes they are just tied up in a back yard with no attention, love, or good care, and die in agony of distemper, parvo or heartworms because their people just didn't take care of them. As an SPCA foster mom I see what problems neglect, not vaccinating, and not fixing an animal, causes.
Please read this lovely story about a little dog who was saved from being a bait dog:
http://www.kens5.com/latestnews/stories/KENS20090525_ktvk-bait-dog-jake-adoption-hurt.774e9ae4.html Pitbulls are not born mean, they are trained that way.
Please if you see, or know of, any animal being mistreated or neglected, please call your authorities today.