Recently spent some time among people not like me - Republicans - and had a chance to get a mild dose of wingnuttery. The topic of conversation was immigration, and while this particular person was married to an immigrant - one of the good ones! - he was overly concerned about all the "bad apples" that were legally or illegally arriving here.
While there are presumably lots of things he might have meant by "bad apples," the most logical one is that they're criminals. In truth, immigrants are much less likely to be incarcerated than native born people.