Taking care of my brother is one thing.. letting my brother steal from me is another. If you want to take a religious point of view on this.. Jesus was asked by the people about paying taxes to Caesar and he responded "Give back to Caesar that which is Caesar's and give to God what is Gods".
So too.. in this case.. the illegals are stealing from us.. they are not putting into the pot.. they are only taking out. Therefore what they are doing is wrong. There is no justice in letting a thief steal from you, is there?