Then perhaps we should help China so they can buy from us! ;-) j/k
I'm sure we had other reasons to build up then stabilize the economies of Europe, with an emphasis on West Germany.
Aside from Europe - The United States initially had more control of Japan's economy - between US intervention and the Japanese government intervention - the fluidity of Japan's Ministry of Trade and Industry (old school B2G/G2B), and the Cold War - Japan's economy flourished.
I'd say preventing Soviet influence was closer to the front burner than whether or not European countries would buy our stuff.
Considering the damage that the Soviets suffered during the war, and considering that it was exerting control over East Europe, how much influence could it have in the West? Sure, some. But I think in the minds of US leaders, getting Western Europe economically dependent upon the US was its best way to prevent Soviet influence in the West.
There was damage everywhere after WWII, as well as a lot of suffering - enough that it canceled itself out when used as a comparative for exerting control over other nation states.
From what I've read, the school of thought was to democratize Western Europe to quell Soviet influence - as well as to prevent an emergence of militarism amongst the populace.
We didn't prop 'em up just to sell 'em $#@! Pete and we're not talking about the Pimp-Ho/Dealer-Crackhead factor either...if we were - that dependence would've lasted a lot longer than the mid 50's, unless we were apt enough to build robust sufficient economies but inept at keeping them addicted >>cough<< - dependent...countries like Japan and West Germany were at the forefront of hindering Soviet influence in that day and age.
I'd say it was probably a bit of both, building up Europe's and Japan's economies so they'd buy from us and starting the Cold War. It's a good thing then Republicans in Congress rejected Truman's wanting to continue New Deal policies and fostered the economic growth at home to help pay for the cost of foreign aid.
Truman showed there was more than one way to skin a cat is all - Congress saying "NO" was only a small bump in the road that you're giving too much credit, hundreds of billions of dollars spent liquidating debt later - toss in the G.I. Bill for good measure, and Korea - then ask yourself "how relevant was Congress during Truman's presidency?"
Truman's autobiography makes for some great reading, the best parts of the book are towards the end, after Truman had already left office.