You can make the broader point that governments ought to be invested in protecting human life regardless if that human is officially a citizen or not.
We are not allowed to kill tourists or other travellers.
Presumably governments can take away your citizenship, and it has been done before, but I think this shouldn't be a de facto license to kill.
I suppose secular people would argue that it is forbidden to kill them without appealing to their soul. And a secular pro-life argument would most likely revolve around the usual justification for why we don't kill other humans.