I've seen a lot of talk on de-extinction in this thread recently, and I thought I'd weigh in. When it comes to de-extinction, the most feasible method doesn't actually involve the cloning of a genetically pure member of an extinct species, rather the use of genome editing to create hybrids that resemble extinct species. After first sequencing the genomes of an extinct species and it's closest living relative, you then compare the two, and insert the most important parts of the extinct species' genome into the genome of the extant species. For example, to create something that resembles a woolly mammoth, you would insert traits such as their fur and smaller ears into the genome of an Asian elephant.
But, personally, I'm of the belief that bringing back the woolly mammoth in particular is an awful idea. It can be assumed that, like the elephants of today, they were social, wide roaming, highly intelligent animals who learned from the examples of their elders. Getting these animals to adapt to life in the wild would be an incredibly long and costly process that would be far more trouble than it's worth.
This doesn't mean I'm entirely opposed to de-extinction however. There are many species I believe, if brought back, would have a positive impact on the preservation and restoration of our current ecosystems. Species like the thylacine, gastric-brooding frog, great auk, dodo, passenger pigeon, Pyrenean ibex, huia, or heck, even animals like the woolly rhino or Steller's sea cow are far better candidates for de-extinction than the woolly mammoths. As long as the focus of de-extinction is on restoring our ecosystems rather than just on the novelty of the idea, I think it has a chance of doing some good.