Yes, it is often coercive and we have certainly supported unsavory regimes. It is worth considering what the alternatives to those regimes are. In Saudi Arabia, for instance, the House of Saud is actually a moderating force keeping the Wahhabist mullahs from taking over completely. Liberal democracy will not work everywhere today, as our horribly misguided experiment in Iraq has demonstrated. I recommend Fareed Zakaria's The Future of Freedom for a discussion of the problem, but a very short summary is that you cannot have a functioning democracy without substantial economic development (natural resource money does NOT count for many reasons) and a middle class that feels highly invested in stability, growth, and trade.
The US government never supported Hitler. America is a free country so of course there were many private individuals and companies who did. No different than how Western academia was extremely fond of the Soviets until the 1950s. The US actually provided massive aid to the allies before entering the war, through the lend lease program among others. The fact is that it wasn't clear at the time that it was in the United State's interests to oppose Hitler. It was a far away problem, there was a strong isolationist mood in the US, and even the Brits were trying their hand at coexisting with him.