I have to disagree with some of you. First, if we caused the extinction, and what we did has been corrected, then we should do all we can to bring that animal back. If it went extinct of natural causes, then leave it alone, I think it would be a losing battle. I also don't think we should bring something back as a novelty.
Think about it this way....it was not that long ago that whitetailed deer and turkeys were extinct over much of their range. If we had left nature alone, then we would not have them now.
Admittedly, some of the species listed have no place in our current landscape. There is not a place for the smilodon, mammoths, mastodons, or passenger pigeons to name a few. There simply isn't habitat available. Some others we do have a place for.
Aldo Leopoldo said it best....One of the first signs of intelligent tinkering is to keep all the parts.