Open borders without anyway to know who is here is not a good way to go

If I leave my house unlocked and hang a sign on the door "Come on in" is it not reasonable to expect that I might get all sorts of people? Would I have any way of knowing anything about them? Would I have any recourse if I was robbed or vandalized? I wish that someone could articulate in a coherent, logical, factual way why our Country is any different. I really would like to understand how open borders without anyway to know who is here is a good way to go. I'm talking immigration not refugees. They may or may not be different but I agree it is a different situation and requires a different discussion. I am not against immigration. I am against illegal entry. I have yet to find anybody who can tell me why I am wrong.