OK, Joe, I'll ask you a question:
Why do you attempt to create moral panic by quoting fictitous scenarios, forming hypothetical questions, and finding over-simplistic soultions?
A simplistic answer to your question, I say simplistic 'cos that's the level that you wish to persue the discussion. In reality, it's multi-faceted and complex;
If, anyone wants to enter any country with the expressed intention of abusing the system, then it's morally unjust.
But a) to my knowledge, there have been no instances of the type that you quote, b) any similar instances will not be as simplistic as you would like to think, c) while I have considered it unjust, it may not make it illegal, therefore not worthy of your persecution of innocent individuals, d) even if it were illegal on a small number of occasions, and I emphasise IF, it still would not justify your persecution of a number of individuals who may or may not be immigrants, e) even if they were immigrants they may be here completely legally, and finally f) they may have brought considerable benefit to this country and its people.