I simply read your post to make it make sense. That is, you’re saying “America is a nation of immigrants” to refer to some articulated principle—like free speech or property rights—that should compel the electorate to adhere to some policy going forward.

If by “nation of immigrants” you mean merely the fact that most Americans have immigrant ancestry, your original post makes no sense. Why would that incidental fact have any bearing on what America’s immigration policy should be going forward? Mere accidents of history don't compel a democratic republic to maintain any particular course.