I'm not naive enough to believe it was because we were the "good guys". It couldn't have been very popular with veterans and their families. I've always been curious about this, as it seems to go against how one instinctively would deal with a vanquished foe.
Concerning Germany you have to see that Germany after WWII was an ally and not an enemy anymore. Also Germany was the direct border to to the GDR and other communist states. So a strong Germany was an advantage to the NATO instead of a weak one. Also Germany Industry specially the Steel Industry was one of the biggest in whole of Europe and having an economically stable Europe was also in both the NATOs and the USAs favour
Because 30 Years earlier, directly after WWI nobody helped anyone building something up. The following economical crisis was the fertile ground for extremists to rise. Germany was punished hard and had an awfull lot of repairments to pay, which they couldn't. So during the crisis years they had to give money and goods, though they hadn't much. This lead to an hatred against the victorious powers, which was one thing that helped the nationalists party to gain power.
Of course there was more, but this was one mayoe concern. Then there was the "democratic aid", especially the US wanted to help Germany to build an working democratic system. This was not the case in the Years 1918 - 1933 where the german population was not relly happy to be in a demcratic system. And then there was this fear of a comunist revolution, that's why the US aided Western Europe with the Marshall plan, but nothing behind the iron curtain ( a term which was first used by Churchill in 1947)