Mark Kleiman has some wise thoughts on the conservative establishment's hatred of Mike Huckabee. It should also be said, however, that on a more basic level a Huckabee nomination would be an electoral fiasco for the Republican Party. Not just in the race for the White House, but down ballot as well. If you're Gordon Smith or Susan Collins or Norm Coleman the difference between the Republican nominee being Romney/Rudy/McCain or being Huckabee is enormous.
Whenever the Republican Party is in trouble, it's always worth revisiting Christopher Caldwell's classic 1998 Atlantic piece "The Southern Captivity of the GOP". The past nine years have, in many ways, run against Caldwell's thesis. But I think the best way of reading him is as offering not a prediction as such, but a kind of warning: Given the size and distinctiveness of the South as a region, and given the GOP's dominance of that region, the party is perpetually runs the risk of becoming a merely southern party.
The most successful Republican politicians of the "southern strategy" era, Richard Nixon and Ronald Reagan, were Californians who were personally indifferent to religion and both led political coalitions that extended far beyond the south and its brand of evangelicism. Bush, in keeping with the more modest nature of his political coalition, is a Texan able to present himself as southern to fellow southerners. But on the national stage he overwhelming identifies himself with the iconography of the West -- cowboy boots, clearing brush, a ranch -- rather than with the south. And, again, for all his political reliance on evangelicals, he's actually a Methodist.
A Huckabee-led Republican Party would, even if it got its act together and started offering a well-briefed candidate with cutting-edge policies out of the conservative think tax universe, be very very very Southern and not even in a particularly "New South" kind of way. You could pull this off, perhaps, under generally favorable political circumstances, but given the bad overall climate it'd be a recipe for disaster.