You make a good point that someone is doing this to us intentionally, the question remains, what do we do about it?
The first step in solving a problem is to admit you have a problem. I don't think most Americans believe that our cultural, economic, and demographic destruction is deliberate. So the first step is to raise awareness.
Once enough people are aware we can simply arrest those that are doing this and put them on trial. If the authorities won't do it then we have to remove the authorities and put people in there that will.