He is interested in these analogies because, as a society, we understand that sexism and racism are unfair ways to evaluate differences between each other. They are destructive forces.
In a way, the speciesism argument has merit because empirically or from a secular perspective, there is no reason why human beings have a right of protection over other species.
But, from religious perspectives, there is a reason, i.e. that humans have been blessed with a right to seek food and livelihood at the expense of other species within reason. Religious perspective - like sanctified slaughter or the blessing over food (i.e. Kosher, Halal or Christian past traditions to not eat meat on certain days) however is meant to curb the speciesistic attitude. So, there are different underlying presumptions here.