Awhile back, someone posted a link to a video of some fellow at the War College talking about Lee's foray into Pennsylvania. It was quite good.
He attributes Lee's loss to a dispute between two of his Generals, I believe Stuart was one of them, and I forget the name of the other.
The man's point was that they hated each other, and when Stuart was to make his circle around the Union ranks and then meet up with Lee, he ordered rookie sections of Cavalry to accompany Lee, and he ordered the seasoned sections of cavalry to remain to guard some pass or stretch of land, because he hated the guy in command of them.
Lee had previously demonstrated that he would not use unseasoned rookie cavalry, and Stuart knew this, and if Lee had had the seasoned and successful group of cavalry that Stuart had ordered to remain behind, he would have used them and it would have turned the tide in Lee's favor.
The man's point was that Lee lost Gettysburg because of a grudge between two of his subordinate Generals.
I think I found it. Here it is.
One of the lamer reasons I have heard for Lee’s loss at Gettysburg. It was Lee that gave Stuart the option to choose his own route into Pennsylvania. Lee never envisioned Stuart riding a circle around the Union Army.