What do you think about Singer's argument here that if we are to avoid speciesism, we must at least consider doing to human animals what we now do exclusively to non-human animals -- assuming both have similar levels of sentience or the ability to feel pain.

Why, in other words, would one think it is moral to experiment on a conscious adult rat, dog, cat, or primate, yet never even contemplate experimenting on a human being with a similar, ora decreased,level of ability and sentience?

Does the "Argument from Marginal Cases" work? Please explain.