Why was James Longstreet called controversial?

Answer 1

First, he was often at odds with his commander, General Lee, especially during the Pennsylvania campaign. Although he respected Lee, and said after the war Lee was the war's finest General, he often tried to impose his opinions on Lee, such as at Gettysburg when he insisted the Confederates should move around the Union army's right flank to interpose between the Federal troops and Washington, forcing them to attack entrenched rebel positions.

Earlier, at Second Manassas, he had positioned himself on Pope's flank while Jackson's men were holding Union General Pope's army off behind a railroad cut, some men out off ammo were throwing rocks at the Yankee attackers. Longstreet took his time, and Jackson was nearly overrun. But he finally rolled forward, and crushed the Federal flank, winning the victory.

After the war, he also embraced Catholicism, unheard of in the south at that time.

For his shortcomings, he was Lee's best corps commander after the death of Jackson, and was instrumental in many southern victories.