I have always found that construction meaningless. One of the only three? One of the only three million? Without some reference point, “one of the only” doesn’t tell me anything.
I used the phrase “one of the only” because the exact number of herds considered “wild” varies from author to author. I have usually heard the phrase “one of four”, with the four being Yellowstone, Wind Cave, the Henry Mountains bison herd, and the Elk Island herd in Canada. Except, as has been noted in this thread, the Wind Cave herd is fenced in, the Elk Island herd is fenced in, and the Yellowstone herd is artificially confined through use of natural landforms. However, I’ve also heard “one of seven” and other numbers of supposed free-ranging herds, and there’s no consistent definition of what herds are considered wild beyond Yellowstone, Wind Cave, and Henry Mountains always listed. So unfortunately I cannot be more precise.
Which would be useful for making a point about today’s concept of “conservation.”
Deleting the entire megafaunal population of a park the size of New Jersey that is allowed to function on its own just to make a point doesn’t help anyone learn anything: it’s merely an argument in semantics. It’s basically deliberately creating a problem for other people that no one asked for and trying to justify being obnoxious. There really isn’t anything in nature that hasn’t been affected by humans in some way. Even populations of wild game like white-tailed deer are heavily managed, and humans do take steps to manipulate the populations of many native species. Most visibly terrestrial megafauna, but you also see this in things like the initiative a couple of years ago to plant more milkweed to boost the monarch population.
Indeed, while the observation that everything is affected by humans to some degree is useful, it ties into a broader problem that I have heard several wildlife biologists mention in that if you only define things that have no trace of human influence as “wild”, it encourages people to think of large swaths of the planet as “not wild” and therefore not important for conservation. Wildness becomes defined as “other”. This results in people not caring about local conservation efforts or wildlife closer to urban areas compared to wildlife in the Amazon or the Serengeti. Despite the fact that conservation in these areas is important for maintaining sufficient habitat area for many species. It also results in a dangerous dichotomy which defines anything humans do as unnatural, which not only teaches people humans cannot coexist with wildlife on planet Earth (and this is an increasing problem among public perceptions of nature) or that improving local environments is pointless (i.e., we can’t remove a city, but it is worth replanting forests and removing old dams). This is one of the reasons behind the big push for “urban conservation” and awareness of wildlife in anthropogenically influenced areas in the last three years or so, to try to bring attention that “wildness” is not restricted to far off, out-of-sight lands.
Good example of this is when conservationists initially started the breeding program to save red wolves, they aggressively purged any red wolf that they believed to be “tainted” with coyote or gray wolf genes (Dan Flores’ Coyote America is a good source for this). And I do mean purged, they wouldn’t even allow hybrid red wolves that were housed in zoos to live out their lives in captivity without breeding. This ended up wiping out the vast majority of the surviving “red wolf” population (only 14 out of 400 individuals known survived). Then genetic studies have found out that red wolves arose via an introgression event between coyotes and gray wolves, and that may have been due to environmental changes driven by Native American populations (specifically, deforestation by people like the Mound Builders allowing prairie taxa like coyotes to expand eastward and breed with gray wolves).
So in the modern day conservationists may have accidentally killed off the majority of the surviving red wolf population in the name of “purity” (since red wolves naturally interbred with both coyotes and gray wolves anyway), and may have even removed key red wolf genetic variation from the gene pool (surviving red wolves are very inbred). Conservationists’ obsession with genetic purity is also one of the biggest roadblocks to restoring red wolf populations. Red wolves right now are restricted to this tiny area of northeastern North Carolina, because if they try to introduce them anywhere else the red wolves immediately start trying to breed with the local coyotes. This is why there is great concern the red wolves will get wiped out by climate change, instead of, say, moving them to a place like Smoky Mountains National Park where they used to roam. Additionally, the current obsession with restoring everything to it’s “natural” (read: pre-human) state has made the conservation of the red wolf a hot-button issue, because researchers fear if the red wolf is known to have arisen as a hybrid no one will want to preserve it anymore (and some anti-wolf advocates have actually used this argument to claim the red wolf should not be preserved).
Removing entire populations of animals that the vast, vast majority of people would consider close enough to wild to be indistinguishable would be entirely unhelpful for this, and on top of that would go against some of the major goals of iNaturalist, which is to help people learn and be aware of wildlife more generally. Few would consider a more-or-less self-sustaining ecosystem spanning a 19,000 square km area the size of Puerto Rico and Cyprus combined to be “captive”, and defining it as such seems needlessly contrarian.