Highly-skilled, legal immigrants and ostensibly low-skilled, illegal immigrants are two different groups of people with different motivations. Low-skilled immigrants contribute to different kinds of jobs (e.g. agriculture, construction, domestic work) than the ones highly-skilled, legal immigrants do. A family swimming across the Rio Grande, trying to escape destitution in Venezuela, probably isn't going to take a programming job from the man or woman from India, who came to the US on a work visa.
