There is some truth to your statement. For example, we will never know if PG would shut down HN if required to hand over the private logs. So yes, our posts can be cross-referenced with other online profiles, etc.

Now, should the conclusion be "we should stop communicating electronically"? That would be a severe restriction to free speech and thus advancement of our species. So, no.

Maybe the right direction is to migrate the discussion towards encrypted and distributed forums. RetroShare offers such a feature (amongst others): http://retroshare.sourceforge.net/