They see only the relative merits of the illegals being here. They see that being here, doing the work "that Americans don't want to do", which is a crock btw, is better than anything they have in Mexico, Guatamala, etc. It may be, but supporting them here illegally also supports them being here as a second class of human being. The thinking they won't admit to is, "Yeah, they're at the bottom of the classes, but at least it's better than Mexico." The point is that they don't mind seeing them as a bottom class.
If they really cared about these people they would urge them to go home and work to institute change within their own failed governments.