By providing the appearance of an escape clause, so-called de-extinction could undermine not just the few protections that endangered species have but also the idea that we need to make any changes at all.
That's the big concern. It seems like the goal of this project is to underwrite an attitude of "who cares about extant species that are currently threatened? We can just resurrect them if they go extinct", ignoring the facts that (a) no you can't, (b) it would be way easier and less time and resource consuming to prevent the extinction in the first place, because (c) you'd be resurrecting them either into a zoo or the exact conditions that caused the extinction.
We live in a profoundly stupid culture that acts like there's nothing wrong with breaking something if you can fix it and which vastly overestimates its ability to fix things.