How to prove Poaching Animals is bad?

I'm making a film and in it, it deals with the molarity of poaching and goes against it. Now I know the obvious side effects such as the decrease in biodiversity that can effect us all and other things like that, but how can I prove this without making it too preachy and to make it appeal to some people who may disagree with the message? How can it be persuasive? While it will mention the science, how can the message be transfered to, I suppose, a close minded person?