This thread seems full of people who are arguing at cross-purposes. Iolis is correct in that there are times when (and I REALLY hate to admit it) the EU, (stinking undemocratic etc., etc.) actually is of use to provide occasional checks on the national government, much to the annoyance of (particularly) the previous pack of traitors in power. Iolis' post, had you read it carefully, is correct and he just uses precise language to describe it. You point 4 is utterly correct, and most of point 3 is also demonstrably so.1. Diplomacy is generally taken to mean all interaction between states short of war. Pragmatic reality may be a part of it but then again, Hitler's foreign policy from 1933-38 was built largely on bluff.
2. The rest of your post is just high blown tosh with phrases like 'Dicean principle' thrown in to impress the feeble-minded. As far as 'National Sovereignty' is concerned, what we have and have had in the past may not be perfect but it was subject to Parliamentary review and the Parliament was a British Parliament elected by British people and, despite your scepticism, it proved remarkably responsive to the electorate and ensured that Britain was one of the most politically stable societies anywhere in the world for the last 350 or so years.
3. Supranational bodies are materially different and, as an electorate, we are linked to them only indirectly. I am at a loss to think of any freedom bestowed or guaranteed to the populace of the UK due to our subjection to a supranational body though I can think of numerous historical liberties which have been curtailed thereby and the foulness of the European Arrest Warrant may stand bail for the rest of them.
4. Any grouping not accountable to the democratic process is, by definition, undemocratic, and therefore, I would argue, nothing we should base any of our liberties upon. We have never be so subjected to supranational agencies as now and, no coincidence, the state and its agents have not had so much power to interfere in our lives since the reign of James II. Please remind me, how many government agencies now have the right to enter my property without a warrant compared with thirty years ago?
Your point (1) might have been disputed by the Wehrmacht, who weren't exactly bluffing. Hitler may have been prone to making mistakes which cost his country dearly, but at the outbreak of war between the UK and Germany, he didn't really need to bluff. I don't agree with point (2); it used to be the case, but in the last fifteen years, the national and EU parliaments have been as undemocratic as each other, as you yourself subsequently state.
The fact that Iolis is correct in that one could play off one undemocratic body against another to an individual citizen's benefit on occasion, does not make your points (3) & (4) wrong.