Illegal aliens benefit the rich, creates more dependance on government, "grow" the economy, grow the government, and support the left.
They also put downward pressure on wages, drive up housing prices and degrade public schools and public services. But these things only hurt the working poor and middle class, so the left does not care.
Remember, the rich elites never suffer the consequence of their ideology. If gasoline goes to $50 a gallon, they don't care, just less traffic for them.
Their kids aren't going to public schools, and they're not having to stand in line at the emergency room.