This debate over
whether or not to refer to MS 13 members as "animals" has weirdly reversed the positions of the left and right. The left has normally taken themselves to be the descendants of the heroes of the Scopes Monkey Trial, and thus has argued that it is
good for us to recognize that humans are merely another kind of animal. Seeing humanity as separate or special leads to 'anthropocentric' thinking, they normally go on to argue, that blinds us to the fact that animals are much more like us that we are prepared to admit. Vegetarianism and veganism, as well as animal rights arguments, rooted in this basic approach are far more common on the left than otherwise.
The right, meanwhile, has normally advocated the orthodox Christian position that humanity is categorically different from animals: that we, alone of creation, were made in the image of God. In addition to serving to ground laws that tend to follow Christian doctrine, this tends to root right-leaning doctrines of conservation (rather than environmentalism), good husbandry (rather than veganism), and the like. The idea that man is special, and placed on earth with authority over it, arises here.
Of course these days everything is about Trump, and the fact that he said it means that one group must defend it and the other oppose it. Principled arguments are not as common as once.