While it was relatively easy to immgrate legally 100 years ago, rules were still in place to prevent potential immigrants from becoming a burden on the people here. People who were lame, completely indigent, mentally retarded, infected with chronic contagious diseases, unmarried and pregnant were all shipped back.
The 25% over poverty is attempting to serve as a similar requirement today. They come here illegally, and then require us to spend huge quantities of already excessive social services dollars to take care of them. This is wrong.
Also, Mexico has long turned a blind eye towards problems with our shared border as long as they restricted their harm to the United States. Whether it be outlaws, marauding Indian tribes, or illegal immigrants, Mexico has pretty much allowed them to do whatever they want as long as they do it here.
That said, I think we need to enforce the immigration laws we have. There is no inherent right to live here. This means we make a defensible border. This means we hunt down and send back those here illegally. This means we require a baby to have one parent here legally before the baby is a citizen.
Is it in our national best interests to make immigration requirements easier? Is it in our national best interests to expand immigration? These are questions that we need to pursue, but do not have obvious answers.