“For example if a Mexican immigrant does your gardening, you have more time to read, study and spend with your family. He’s grateful for the work and you benefit too.”

What about the gardener down the street who is an American citizen who can’t get a job because the immigrant comes over and takes less pay (under-the-table). If the average person has to choose whether to pay $100 to get their lawn cut by a citizen or $50 by an immigrant, guess which they’ll choose?

“If a foreign scientist comes to America, he helps develop technologies that benefit us all.”

I really don’t think this is a valid argument. How many scientists do you know that are climbing the border fence in San Ysidro so they can come develop technologies here? I don’t think anybody is arguing against foreign scientists legally coming over here and practicing.