Robert E. Lee was already a living legend in the South when he decided to invade Pennsylvania following the great Confederate victory at Chancellorsville less than a month before. No Union army had ever defeated him in battle (the strategic draw at Antietam notwithstanding). James Longstreet was an admirer of Lee and a career soldier. What you are suggesting--that Longstreet attempt a mutiny or coup d'etat against his commander--would have gone completely against his military upbringing, and I'm sure that Longstreet NEVER considered this option. First, Longstreet would have had few supporters to follow him. Although he may have been able to convince a few high-ranking officers that Lee's plan to assault the Union center had little chance of success, Longstreet would never have been able to gain enough support to supplant Lee--especially from the rank and file enlisted men who worshipped Lee. The Army of Northern Virginia had experienced so many great victories against their Federal foes that Lee believed--as did most of the other soldiers--his army was unbeatable. Mutiny and dishonor were not part of Longstreet's makeup; Lee's reputation was beyond reproach; and the men who made Pickett's Charge were extremely confident that they would succeed in this glorious attack. A mutinous action by Longstreet would have been not only unsuccessful, but he would have been executed for making the attempt.