(2) was intended to proactively dismiss one specific attempted "gotcha" that I hear often in response to this view: people think I'm saying that it's okay for
minority cultures specifically to die out, and that I would feel differently if it was American culture being overtaken as a result of high birth rates in some other country and low birth rates in the US. This is not what I am saying. I don't think American culture is special.
> Are some groups "allowed" this, and not others?
So no, my position is that no groups are "allowed" this.
Another way I can express this, that may be more clear, is that a culture isn't a thing on its own. It's a description of the way its members live. Those members may be very attached to that way of life, and it is immoral to take it from them (see (1) above), but the question of whether new people start living in that way is morally neutral.