How come scientists are trying to bring back dinosaurs?

For starters, we don't know a lot about dinosaurs. We used to think there was a brontosaurus, until we discovered someone mistakenly spliced two different dinosaurs. Some scientists think the T-Rex might have had feathers and some think the T-Rex was not a hunter, but rather a carion eater (like a giant wingless vulture). So, bringing them back would give us an opportunity to study them more to better understand what these creatures were like. Simply bringing an extinct creature back (dinosaur, carrier pigeon, dodo or whatever) may be a great achievement in its own right. Dinosaurs may have genes that could prove usefull in treating diseases. Depending on the type of dino, they might also be a viable food source - for example, suppose a 2,000 lb herbavore dino consumes some easy to grow plants that could make it less costly to raise than an 800 lb cow - might be a means to produce more food for less. Their skin might be a cheaper and sturdier alternative to alligator and snake for belts & such. Some dino's might make good pest control (catch mice and other small critters) or they might be trainable as pets (smaller ones most likely - no velociraptors). They might also make more challenging hunting game. Many dinos would be disastrous to their local eco systems as they would instantly become a dominant predator with little or no competition, which makes dino restoration something that would require a very controlled and well studied process to avoid major disaster. It may prove to be a case where some dinosaurs are ok to revive and re-introduce while others would be strictly limited to scientific caged study (possibly only growing tissue samples only), or avoided entirely.