Lee was a sober man, and attacked because he thought he could win. He thought the Army of Northern Virginia was invincible. If his (vague) orders had been properly followed on Day 1, things would have turned out differently. Jackson could interpolate Lee's orders so that "attack if practicable" meant "drive those people back into Hell where they came from!"

That said, I think Longstreet was right. What is sometimes forgotten about Longstreet at Gettysburg is that he advised Lee to change his plans twice - at the Round Tops, he wanted to flank to entire position by threatening to occupy the big hill and establish artillery there, then moving around them to threaten the Federal rear, instead of Lee's choice to make a direct frontal attack on entrenched Federals on the small hill. Longstreet's goal was always to make the Yankees attack *them* on ground of their own choosing - and I think it was correct at the time. Of course, Lee later adopted just this strategy with great success against Grant, but Grant knew that he could bleed Lee dry no matter what he did - by the time Lee understood that Longstreet was right, it was too late.

Poor Longstreet - he deserved a better fate.