Then explain to me why, if in OTL they allowed Germany more than a little, it follows that they would allow even more. 'Cause that's your whole argument.
You have missed my point in the Apples and Oranges commnent, it seems. Your comparison between Germany/Japan and Austria/South Korea is completely faulty since the Korea had had a completely separate national identity from Japan for centuries and the vast majority of Koreans hated the Japan domination. West Austria could be described as having a strong regional identity, much like Bavaria, and it is very very questionable that most Austrians would oppose a second Anschluss in these circumstances.
Denmark and Iceland were not in a good position either.
They lacked a land border with the Soviet bloc. And the Soviet threat was 98% a land one up to the 1970s.
Same goes for the Benelux if the Soviets overran West Germany.
If the Soviets overran West Germany NATO would be hours or days from using nukes.
They allowed a limited rearmament of West Germany out of fear of the Soviet Union.
Limited in the sense that the Bundeswehr was not allowed to own WMDs, yes. Failed to see much of limitation otherwise.
Uniting West Germany with West Austria does not strengthen NATO against the Soviets - keeping 2 different German states would result in the same military might.
Yup, sure, the armies of two allied state train, supply, and develop just as well as if you unify them in the same state, the massive benefits of integration and standardization have just disappeared. Not to mention the benefits from complete integration of the economies. Guess the USA ought to scrap the Constitution and restate the Articles of Confederacy, since who needs national unity to stay a great power, you just need a good alliance treaty. 


But if the Germans ever become a menace to European peace again, something which was feared in the West, reasonably or not, then uniting West Germany with West Austria is simply a lousy idea.
There were far more clever ways of keeping the Germans into line, without harming their effectiveness as anti-Soviet bastion.
Empty guarantees if the US withdrew its forces from Germany or an agreement was reached with the Soviets on a neutral Germany or anything else happened which could not be predicted in 1949.
If the USA would withdraw its forces from Germany (effectively putting an end to NATO and hance the whole cornerstone of their foreign policy) or would agree about a neutral Germany, then such massive butterflies would be at work that the union would strategically trivial.
Besides, who said the union had to happen specifically in 1949 ? it could happen later, as it was with Saar. In mid-late 1950s concerns about German resurgence had diminished greately.
France opposed the strengthening of Germany on principle and Italy did not want to border Germany while it had to deal with the Germans in South Tyrol.
Italy would only be concerned that Greater West Germany would confirm the DeGasperi-Gruber Accords that recognized Italian sovreignity in South Tyrol in exchange for large autonomy for the local Germans. Something that West Germany would have difficulty to do. As for France, they need German goodwill once European economic integration has started, and if America okays the union, they shall simply be overruled. That France was a nominal victor power of WWII was but a polite fiction of the Anglo-Americans.
This is besides the general European fear of having to fight another World War against Germany.
Steadily dwindling by the years.
According to Kissinger in 1989 Mitterrand talked to Gorbachev about a common front against German reunification. Gorby, too busy at home for such an active foreign policy and probably hoping for German aid (which Kohl did later give to the Soviet Union and Russia), said no.
Allow me to show the deepest skepticism about something that would be effectively the 1989 French President having a Nixon moment and proposing a treasonous complete betrayal of the very cornerstones of French national security and economic livelihood for two generations, namely NATO and EU, to indulge into an ASB anti-German scheme.