Europe in total equals the US by numbers: population, GDP, military availability (though obviously not cohesiveness). It's not that the US wanted a weak Europe; they wanted weak individual states depending on each other and the US for collective security. No, it was never an alliance of equals; that's not the point. Collectively, NATO was incredibly strong, and what Europe offered was the battlefield. In the Cold War, the plans were that the Warsaw Pact forces would come streaming through the Fulda Gap and burst through NATO defences, crossing plains to the Rhine River and surging westwards across Europe. The NATO plan to handle this was to detonate nuclear land mines in the mountain passes, blocking them.
The NATO plan was to detonate nukes on German soil to take out the initial advance and block the second echelon of Soviet tank divisions (without Soviet nuclear weapons, tactical or otherwise, having been used). Germany OK'ed this plan. Upon detection of an imminent Soviet attack, special forces would, 12-24 hours in advance, emplace the nuclear mines (about the size of half a minivan) and prepare to detonate. NATO's warplans always anticipated first use of tactical nukes (because NATO numbers were always dwarfed by Warsaw Pact numbers) and the battlefield was always Europe. Every warplan always involved European allies taking the first blow and America responding.
Calling European states protectorates that begged for American protection really undersells the value of a relatively independent (western) Europe, both economically and militarily. Without Europe as the front line in a future war against the Warsaw Pact, America would either have to watch Europe be subjugated by the Soviet Union, or fight a war across the Atlantic without local cooperation (and the Pacific, where Japan/South Korea stood in for Europe). Europe offered intelligence co-operation and direct contact. Economically, Europe (and Japan) rebuilding quickly and participating in first world market economics was unbelievably beneficial to the US. If nothing else, the fact that the US dollar is the world's reserve currency is justification enough for US expenditures in the Cold War.
To go back to my original point, it was always mutually beneficial, and everyone knew it and was in agreement. Everyone was stronger together, and no one is in debt to anyone else.
If the cost/benefit calculus has changed, then that's just life: shit changes. All of the problems you mention are exclusive of America's (previous) commitment to NATO--American has more than enough money to attend to both. But the idea that Europe/the rest of NATO should suddenly be a defense subscriber to the US is just... America didn't bootstrap itself to the position it's in now. Its prior close workings with the free world have made all the difference, and for a while (and no longer) it seemed like everyone understood how it all worked.