You really think Dunkirk was a militarily defensible position? Really? With all due respect, the only reason they got out of Dunkirk is because the Germans stopped the advance, thinking that they could just mop up with the Luftwaffe. An entire book was written on the subject:
Dunkirk, the Patriotic Myth, by Nicholas Harman In short, the Brits didn't want to fight on the continent, and certainly not alone. Panzer attacks never worked against heavily concentrated troops, and the Brits lost more troops by evacuating than they would have by digging in and staying. Quite a few British troops had committed war crimes by using hollow point bullets and didn't want to get caught in France. Others just wanted "blighty" and get sent home. The story of WWII is largely that an avoidable war was fought because the major allies of WWI, simply didn't want to fight. Dunkirk is simply more proof of that fact, which occurred after the long "phoney war".
BTW, you still haven't explained how the Germans held Dunkirk until after VE Day...
Agree that Britian did not want to fight on the continent alone, for their army would stand no chance long term. Plus again Britian was facing a very real chance of a German invasion of their homeland. Once they knew France was done, they had to get out.
As for the Germans in Dunkirk till the end of the war, that is simple. We contained them, which was all that had to be done. As is evident by how the war went after our return. Quite simply, the Germans held it till the end because once they were contained they were neutered. I mean look at the forces we used to hold them there.
Lastly we wanted Antwerp not Dunkirk. Would we have used Dunkirk had the Germans not been there? Almost certainly, but they were there so surrounding and containing was all that was truly needed.