Are closed borders ethical?

I live in Germany.

I’ve been discussing the refugee situation with a couple of people I know from school. We talked about whether closing borders can ever be morally acceptable, and how communities justify shutting fellow humans out.

What are your thoughts? Do you think your country belongs to its citizens, or humanity at large? Does the fact that our ancestors created our country make it ours? What about the aspects which aren’t man-made, like the climate?

One member of the group maintained that the country belongs to the taxpayers. He was very vocal, but I was able to remind him that he has never paid taxes.