The Round Tops weren't discovered by Lee. Lee wanted nothing to do with the Round Tops. His objective was a converging attack on Cemetery Hill. Longstreet was never to attack the Round Tops. They were specifically ordered to attack up the Emmittsburg Road...not to attack the Round Tops. The prime objective was the Peach Orchard.
I think we have to beware of hindsight, in all this. Realistically, we'd have to say that the "objective" of the campaign as a whole was simply to win a decisive victory over the Union Army.
The whole Gettysburg battle was improvised, after all, once the leading units made contact without any orders from the commanders. As the saying goes, "No plan survives contact." In this case, contact came first, followed by plans based on inadequate information; followed, sadly, by sticking with those plans in spite of events.
Gettysburg is a pure tragedy, in my view.
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
I have seen no orders to that effect in any history of the battle. To attack up the emmitsburg road under constant enfilading fire would have been a disaster.
Fine. Still an impossible task. 3 corps (one of which was already badly mauled and one division which was not up yet) were not going to take seven corps (even if one or two were damaged). After fighting through the Peach Orchard, his troops would have been under enfilade fire from both the Round Tops and from the Cemetery Hill line.