The article "Future of Zoos: Cloned Animals, Robots and Cageless Habitats Under Consideration" by the Huffington Post addressed the possibility of bringing back extinct species of animals via preserved DNA. Some believe that through cloning animals that became extinct could be brought back.
I think that there are a lot of ethics that must be carefully debated before bringing back any extinct species. First off, what species would be brought back? Only ones that were extinct by human means or also those extinct due to natural circumstances? Second, the consequences of reintroducing the species into the wild would have to be examined. It is likely that the extinct animals' niches in their former habitat have been filled by some other organism. Lastly, who would have the supreme control and play the role of "God" in determining what gets to walk on this earth? That is a power no one person should hold.
Some may think that it would be neat to have a wooly mammoth roaming the earth once again or even just bringing back a recently extinct animal such as the dodo, but serious ethical questions must be examined before any action is taken.