I disagree, that such name-calling is the only way people argue for the welfare of immigrants. Some people try to make the case that it is Christian, in some obligatory sense, to give shelter and succor and all that. Or Godly and necessary with respect to some other religion. Or merely desirable, decent, and proper, in light of some secular-humanist understanding of how we ought to treat each-other. 

The name-calling is often, I think, a clumsy attempt to imagine the motivations of people who hold different positions. Where opinions are starkly divided, the proponents of conflicting views, sadly, sometimes try to gain a semblance of victory through disparaging, and even mis-characterizing, their interlocutors. Sometimes such mis-characterization may be due to actual ignorance of the other view, and stem from a sincere misunderstanding. In such cases,  sustained and friendly discourse has the potential to widen our spheres of empathy and understanding.