I don't agree to part of your argument.. Assuming that Dyson theory is right, we should be able to observe megastructures if out there there are supremely advanced civilizations. And to date we couldn't see any. And it seems that

However, i agree that we can't communicate with primitive species, but it should be possible with more advanced ones that must have rely on electromagnetic signals. With that said, the problem I see is that our sphere of visibility is at most few tens of light years in radius and that assumes that the weak electromagnetic waves are noticeable at such distances even by advance technologies.