The reason why the GOP is so terrified of Gingrich's attacks on Bain isn't because they're afraid it will stop Romney from winning the nomination (that's a certainty at this point), but rather that they're afraid of seeing Newt put Bain's way of doing business on the table for GOP base voters, in a way Democrats never could.
Bain crushes unions, strips away benefits and ships jobs overseas, buying companies out with hundreds of millions or billions in loans. They then ditches that debt on those stripped-down companies, who can't afford it, leaving many of them out of business or shells of their former selves.
It's bad for America and the elites of the GOP don't want people to hear it, especially their base. Why? Because the elites of the GOP know it, too, but they just don't care.
Walking over the little people to make money is an easy decision for those elites, but not for most Americans. Democrats are already open to the idea that there should be some restrictions on the way companies can do business, but most base GOP voters aren't. If people, especially the GOP's base, understand exactly what companies like Bain does, they'd no more support it than they'd support drug cartels.