The problem with this argument is that it prioritizes the enjoyment of some individuals over others with no real justification. The grey wolf, for example, went extinct in the Yellowstone region in the first place because humans considered it a pest and a threat to livestock and so hunted it to extinction. Clearly these people didn't enjoy the 'diversity' the grey wolf provided. We don't usually give something the force of law regarding animals just because some people enjoy it. For example, the UK has now banned fox hunting even though a great many people found it to be a source of pleasure and recreation. [1] If everyone desired the protection of all endangered species, there would be no need for this law, but the fact that a law is needed to restrain human action shows that not everyone 'enjoys' this biodiversity in the same way.  [1] BBC News “'More foxes dead' since hunt ban”. BBC News. 17 February 2006.