If it is not immoral to shoot dead an intruder into one's house without asking questions, why would it be immoral to shoot dead an intruder into one's country?
I presume that by "an intruder into one's country" you mean an illegal immigrant rather than, say, an invading enemy soldier. Otherwise, I'd answer differently. Does one own one's country in the way in which one owns one's house? I think not, or else I own much more real estate than I thought. Moreover, an intruder into one's house can plausibly be assumed to be a serious threat to oneself. I don't think this assumption is as plausible in the case of an illegal immigrant, all else being equal.