I also see it as a property rights issue, and libertarians are certainly amenable to property rights. The geographical area known as the United States is all owned by someone: individuals, partnerships, corporations, the citizens of a given state or of the entire nation in common. So illegal immigration could be viewed as trespass. We, as individuals and as a group, own the land you're walking on and we don't want you in it. End of discussion. This is no more acceptable than if you were in my front yard without my permission. We would be within our rights to restrict immigration to only Hondurans, only people with red hair, only women...whatever we damn well feel like, because it's OUR freakin property!
I like your explanation.
This was my line of reasoning too, and then scrolled down and saw your post.