It is often said that the best way to preserve a species is to make it valuable. Creating a viable market for endangered plants and animals should encourage landowners to produce more of those "products." Ideally, a successful market is self-regulating/self-preserving. For plants/animals the grower will not sell ALL of his stock, but will save enough to grow more the next year. As long as it is profitable to do so the species will be preserved. In a best case, the population will steadily grow since then the producers will then have more to sell. American bison and alligator are a couple of success stories here. I’m sure Rancho Gordo will have something to say here, as well. The flip-side is a situation where the market is completely banned. If you are banned from selling products from endangered species then they have no (monetary) value to the landowner. If they have no value then the landowner is not motivated to preserve them - he will direct his time, money, efforts elsewhere. The species will be killed off to use the land for other purposes or just allowed to die off on its own. Any demand for the species’ products will just move underground long enough for the animal to become extinct. Think of the rhino here. Limited monetary value to the landowner since all rhino products are banned. Some tourism dollars, but it must pale in comparison to what the poachers are making from illegal ivory sales. Throw in the added effort/money spent to enforce a ban and it becomes an inefficient proposition real fast. Don't get me wrong here... the Endangered Species Act certainly has its place and every effort should be made to preserve our Earth’s remaining species – including regulation if necessary. I'm just saying that one approach actively promotes the independent growth of a species by making it valuable to have around. The other approach forces the species to fight for its survival based mainly on its nostalgic value.