You are correct that literally every species can be captive bred by dedicated individuals. Genetic diversity is important however and there is something to say about some wild-caught animals. In my opinion this should be limited to the very few individuals who actually have the background and resources to acclimate and contribute them to a captive population. For example; surinam toads are often difficult to find and are always wild-caught. It is difficult to breed them but not impossible. Wild-caught animals would need to be used by several keepers with unrelated stock to create a self sustaining captive population. Obviously with species that are more in demand, more WC's would be needed to create a diverse population.