They should.  If you think that the Universe was constructed according to God’s plan it follows that knowingly wiping out species is thwarting that plan.  For creationsists the argument is even stronger. They believe that each time a species goes extinct there is an irrevocable reduction in the total number of species.  The biodiversity argument holds for believers as much as for non-believers.  Having a wide variety of species acts as a stabilizer.  Each time a species goes extinct there is a greater risk for those species that remain. And we cannot distance ourselves from the rest of nature and say that humans will not be affected.  The very oxygen we breathe comes courtesy of plants.I know that there is a relatively small portion of lunatics (I make no apology for my intolerance) who believe in the coming of the Apocalypse and who see environmental devastation as just another sign of the second coming.  Apart from this group, it seems that believers should favor consertation as much as, or perhaps even more than, us non-believers.