If we can get cheaper, better cars elsewhere, it is wasteful and inefficient to produce cars here. We live in a world of scarce and limited economic resources, and we should be allocating those resources elsewhere, rather than trying to prevent dinosaurs from going extinct. "Buy American" is nothing more than a restatement of the commandment to "pay no attention to that man behind the curtain", IMO...
I often run into the same thing on a smaller scale. People say, "buy local." Around here, it's "buy Kodak, because it helps keep your neighbors employed."
But I can buy a product of exactly the same quality for a third the price from Fuji or Canon (depending on the product) and my neighbors are getting laid off right and left, even in those relatively few periods when Kodak makes a profit. So, why am I supposed to buy American again?