The logistics argument is also very sound.
The problem was not just getting ashore. The problem was getting ashore and then doing something useful.
No Atlantic wall. Lovely. So you can get ashore. Then what?
The nut to be cracked in ETO, the challenge of Overlord, was 1) how to secure a beachhead, and then 2) how to build up forces faster than the Germans.
In 1942, and even in 1943, there was NO path to achieving #2.
How are you going to liberate France even if you can get the entire US Army ashore? You have no supplies!
In 1942 you have a German army with 200+ mobilized divisions. All in France? Of course not. But they can build up to whatever level they need by bringing forces and supplies into the combat zone at speed through a fully developed and un-degraded rail infrastructure across all of Europe, with adequate petroleum for their mobile formations, and an air force with large numbers of first-rate fighters and tactical bombers and a great deal of experience in air-ground cooperation.
Against this you pit an American army of 9 combat-ready divisions, all green, with a smaller, inexperienced air force without first-line aircraft. Not looking very good.
Now let's add that critical factor for success: there is no secure logistical flow once you get ashore. A significant portion of cross-Atlantic shipping is still being sunk. And if your supplies make it across the Atlantic, you still have no high-throughput cross-channel flow to France. No Mulberry harbor, no cross-channel POL pipeline, no LSTs or DUKWs for over-beach supply.
If you are lucky enough to get an intact port, you will have daily Luftwaffe raids and U-boats and E-boats queuing up for glory around your harbor entrance. How are your battleships going to help you there? And every escort resource you put in the channel means more losses crossing the Atlantic.
Of course you can't use the entire US Army anyway. Some forces need to remain in CONUS to form the cadre you will use to build your next-year army. To replace your this-year army. Because everything you send into France will be lost. Get 3 divisions ashore, and you will see 3 divisions destroyed. Get 5 divisions ashore, and see 5 divisions destroyed.
Nope nope nope. It was hard enough to go against the Germans when they were at the top of their game and you were not yet ready for the big leagues. Doing it in their arena (on the European landmass), by their rules (no degradation of the support infrastructure feeding their frontline tactical prowess).
A clear recipe for disaster.
-Mark
(aka: Mk 1)