People point this out regularly. Everyone either knows, or doesn't care for the reasons I just stated. It doesn't contribute anything to the conversation.
That's what makes the original comment so unsubstantive, and why I was so critical of it. It doesn't persuade. It's not interesting. It doesn't provide any new information - that same factoid is brought up in almost every discussion about immigration. It sidesteps the whole issue to make a pointless legal argument - very similar to when someone mentions that the First Amendment only protects you government censorship. Yes, everyone knows that, it's not what anyone is arguing about.
The reason I read HN is because many people with many different views write great comments about technical issues. Sometimes we drift off into somewhat less technical issues like this, but often the comment quality remains high. And when it does, it's because we're not writing comments like that.
And to be perfectly fair, my response was clearly not articulated well and also fell into that category - whether I feel that way or not, that's what I take downvotes (it's presently at -4, which I didn't even know was possible) to mean. (Upvotes don't mean the converse, though!) I should have also done better.