I agree with some of what Eaglesmack has to say here, namely about Hitler's own military acumen. Hitler's paratroopers didn't "suck" but there weren't that many of them and they were more suited to commando style operations, like the SAS rather than massive drops. The German paratroopers did pull off some high profile missions, like rescuing Mussolini in 1943 and their combat ability was demonstrated in places like Ortona, Italy, but there wasn't as much need for airborne assaults by the Nazis on a large scale: they had the mainland of Europe and could march/drive where they wanted/needed to go (for the most part)
The other thing is to remember how the German military structure itself worked. It wasn't a (sometimes reluctantly) cooperative effort but one that encouraged rivalries and antagonism among the commanders vying for strategic resources. The German airborne troops were also part of the Luftwaffe so you have interservice rivalry combining with the systemic rivalries of commanders, leading to a mindset that wouldn't think of using the airborne units unless absolutely necessary because it could give a rival a step up. It seems somewhat awkward (if not stupid) but its believed this was at least partially cultivated because Hitler distrusted the "old guard" of the Wehrmacht and used it prevent generals from gaining too much popularity/power/influence.
Now back to the conspiracy side of things...
Do I think there was a desire to make peace with the Germans in some quarters? Absolutely. A lot of people did think communism a more dangerous enemy than the Nazis, especially after Normandy, when became apparent that there was too much pressure being exerted from all sides, for the Nazis to surivive. In the end can we say those who distrusted the Soviets were wrong? They occupied Eastern Europe for 50 years with a totalitarian state, engaged in espionage against their former allies and fought proxy wars across the globe. Some historical speculation also exists that the German invasion of the USSR was pre-emptive: if Hitler would have waited, Stalin would have attacked Germany, but it would have been when the Red Army was better prepared.
Would Allied commanders have launched an invasion on that scale that was supposed to fail? No. Who in their right mind would have expended that amount of manpower and material, thus leave themselves in a weakened position, and trusting the mercy of the Nazis? Sure there were industrial alliances and profiteering (show me a war where there wasn't, and they always have some pretty powerful political connections) but thats a far cry from actively sabotaging your own country's war efforts.
