They aren't allowed to come here, or stay here, because we are compassionate, but because certain of our "leaders" need them to force fundamental changes upon the nation, changes against our wishes, changes they cannot impose any other way.
Unfettered illegal immigration is the stone that will kill our republic, and give the would be dictators the easily corrupted democracy they desire.
Which is EXACTLY why the Left, and therefore our current government, so facilely support illegal immigration from third-world countries.