If they went extinct a recent while ago then obviously bringing them back won't have a negative impact as long as they're released back into their native lands.
That being said, they died out in the first place because of human activity. What's to say it won't happen again?
Now, for those who say they want to bring them back and keep them all in zoos, well, what's the point in that? They have already been taken out of their native lands, to which they will not return, so what's the point of having them in zoos? So we can oggle them constantly? For our own amusement?
Anthropocentricity is what's wrong with us, and that's what we need to change. If we bring them back to rerelease them into their native lands, then great! I'm all for it! But if we're just going to put them in zoos, then there's no point.