So once upon a time - about 30,000 years ago - a squirrel buried seeds in what would become Siberia. Scientists have been able to use tissue from plants found in that squirrel burrow to resurrect a viable plant, Sylene stenophylla.
Pretty. Also still extant in the Russian tundra, so in this case it's not the rebirth of an extinct species. But folks are all excited - this could be the path to bringing back Ice Age creatures like the wooly mammoth and mastodon.
They shouldn't. Yes, it would have major, major WOW! factor. But this isn't their world anymore. Extinction is perfectly normal. It always amazes me that the same folks who tout a nature-focused religion completely ignore some of the rules that are imbedded in nature. Extinction is nature's way of saying that a creature doesn't fit in anymore. That's true whether it's T. Rex or the dodo - they couldn't survive in the world that developed around them. And any creature that has gone extinct that is brought back will immediately be non-native species.
We've had lots of experience with non-native species:
Rabbits were introduced to Australia as food in the 19th century - they are enormously destructive, creating "the grey blanket" over Australia with their numbers.
Kudzu, the "vine that ate the south", was introduced as an ornamental and for erosion control - now it suffocates the forests of the American South and has been found in Canada.
Nutria were brought into the country as fur animals - they are a major destruction force in American wetlands.
Brown tree snakes were accidentally introduced into Guam in the early 1950s - they have now wiped out at least 12 endemic bird species and are hitching rides into other islands.
The water hyacinth, an ornamental plant from South America, has choked waterways all over the globe, killing fish and other plants, and causing native peoples to starve to death because they can't get through the waterways that act as their roads to food.
I'd love to see a mastodon, a saber-toothed cat, a giant sloth. But this isn't their world anymore, and no matter how well meaning the actions that would bring them back into it, that action would eventually have repercussions. We've had enough examples of those sorts of repercussions that we should know better by now.