On an Island in the Sun
There's no way around it: Moreau's island is a giant allegory for society. Prendick even calls the place "the whole balance of human life in miniature" (16.89). Lucky us: that means we can use the island to explore various aspects of human society and culture.
Well, that's great and all, but why explore human society through a make-believe place? Why not just consider society as it is and skip the middle man? We could do that certainly, but there is a distinct advantage of doing so through a fictional island, what we call detachment.
Reality is loaded with emotions, and people can get upset when they believe their worldview is under attack. Just think of any political discussion you've ever heard, ever. See what we mean? Detachment means we can set those emotions aside and see things from angles and views we might usually avoid.
The Evolution Solution
The Beast Folk are us, and we are the Beast Folk. The Beast Folk started as animals, and Dr. Moreau shaped them into people—well, kind of. Likewise, according to evolutionary theory, our ancestors were animals and Mother Nature shaped them into who were are now. Both processes were painful and, in the words of Moreau, "remorseless" (14.29).
And, just like the Beast Folk, we've created a society with leaders, belief systems, and rules. The goal is to live together in a state of relative harmony—excluding, of course, the stuff we do to each other for the sake of good television. But that's totally worth it.
That's all well and good, but there's a problem. Because the Beast Folk were once animals, their animal instincts sometimes break through, and they revert to their old, natural ways. Likewise, human beings are animals too, and sometimes we can do things to each other that are just downright bestial. Murder, rape, mob rioting, war; these are just a few examples of the old inner-animal rising to the surface.