Not specific to iNat, but I know of two cases of illegal pet traders using geotags on Instagram posts to find and target populations of Spotted Turtles and Reticulated Flatwoods Salamanders.
Additionally, before Black Rails were listed as a sensitive species on eBird, there were serious issues of unethical birding, particularly the use of broadcasts on breeding grounds (to the point where a breeding population was at severe risk from the near-constant disturbance; the location ultimately had to be closed to the public and temporarily guarded).
I think there is a lot of nuance here. eBird and iNat data has been invaluable to some of my past work. I think both sites are pretty responsive regarding concerns around sensitive species. But I do think it is something observers should also be conscious of.