The "right to life" is seen in the objection to a government killing a citizen for no reason. The argument is that, self-evidently, it's wrong for a government to do that. So there must be a right to life independent of the laws of a country or the whims of its rulers. Sure, a theist would claim that God would in particular object to capricious killing, but you don't have to be a theist to claim it's self-evidently objectionable.
And I guess you can argue that some do not recognize universal rights, but it's not a compelling argument to just point out what some people think.
And I guess you can argue that some do not recognize universal rights, but it's not a compelling argument to just point out what some people think.