It's their agenda, and their obsession.
We are at war in the Middle East with terrorists, but these people are pissed off that our Armed Forces are not doing something more important like shooting Mexican campesinos at the SW border.
The shortsightedeness and attachement to that single agenda is astounding. The fact that some would even advocate losing the war over it, well, I can't fathom it.
I'm sure there are people who are sincere in their wish that terrorists should not have the ability to enter America at will, but I am equally sure that there are some who only use that as an excuse.