"Getting weeds out of the national parks is an endless war that can never be won, but many Park Service employees are willing -- and happy -- warriors (HCN, 10/17/11, "Among the processes of place")." This strikes me as rather biased. It is possible to remove invasive plants from many areas, or to keep them under control for long enough that they will obtain natural predators and start "playing fair" in ecosystems.
It is possible to control invasive plants, but it requires people taking a more active role as parts of ecosystems, even those in national parks. This is not a bad thing if done properly. After all, most areas in the Sierras -- and just about everywhere else on the continent -- were managed by Native Americans in a variety of ways for a very long time. As with other issues facing the parks, the ideas of wilderness and 1970s-style environmentalism may actually be a detriment.