One thing, letting GM fail would have had one lasting effect. Manufacturing jobs that we lose tend to never come back. Over the last 5 decades or so we have been steadily de-industrializing in this country, farming out more and more of that to Asian and Eastern Europe where labor is cheap and regulations are loose.
Yes, some European and Asian companies are slightly filling in the gaps there, building stateside factories (cause labor here is cheaper than in Japan/Germany) but it's hardly enough to offset the loss of a manufacturing juggernaut like GM.
bailing out GM was about the least objectionable of Obama's economic policies.