It's nonsensical. I can accept poisoning the blood, but I don't see why illegals do that any more than other immigrants.

I don't know if this is what he was thinking, but if he articulated it this way it would be correct: Illegal immigrants have a tendency to be the people that would be rejected at a port of entry. So they are worse, on average. Much more likely to be criminals since that's grounds for getting denied entry.