Lee really needed to win this battle and I suspect that he gambled that using the sledgehammer approach was his best option. I'm sure he knew that even if sucessfull, it was going to be costly. Longstreet, from everything I have read, wasn't a happy camper, even years after the battle. Pickett on the other hand, wanted to get his name in the history books and saw this as his best chance to achieve that goal.
Tom
Lee wasn't using the sledgehammer effect. He was applying strategy that had worked in the past. Gettysburg was not to be Fredericksburg. It was to be 2nd Manassas in the planning and the initial moments. Pickett's men could not stand up to the flanking fire and therefore the line disintegrated... the disintegration of the line has become, to historians, Lee's strategy.