Save endangered parasitic species?
Although we think of parasites as harmful and tend not to consider them for conservation, they do peform valuable functions including population regulation and the development of immune systems. More philosophically, under the 'intrinsic value' argument sometimes used for conservation, every species should be considered to have an intrinsic right to existence, regardless of its ecosystem function, harmful effects on other species or appeal to humans.

Conveniently, this article has just been published on this very subject. :)