I hear (but mostly read) a lot about the sheer bravery and courage emitted by many Confederate brigades such as the famous Texas Brigade, a Confederate brigade known for its tenacity and hard-fighting spirit, the Louisiana Tigers, described as "fearless", the Alabama and Stonewall Brigades, and many of the Confederate troops that took part in actions such as Pickett's charge (Antietam comes to mind). It seems that Confederate troops, while less well equipped, on average seemed to be pretty brave and courageous in most of their engagements.
Assuming this is true, how come? Why were the Confederates so high on morale and spirit in comparison to Union troops? Was their passions to defend the South, the inspirational and motivational abilities of Lee, Jackson, Longstreet, etc, or something else?
Or is this simply a myth born out of the legacy of the singular Texas Brigade and Louisiana Tigers and then extrapolated for all of the Confederacy?
Where exactly did you read someone extrapolating the Louisiana Tigers reputation to the whole Confederacy? One might as well extrapolate the Iron Brigade of the West to the whole Union army.
Both Confederate armies and Union armies had periods of high morale and low. Sherman's army had very high morale chasing Johnston into Georgia, while their opposite number were dispirited. In the Battle of Missionary Ridge, Union forces charged uphill against orders and routed a Confederate prepared line. In the Battle of Fredericksburg, they followed orders and marched to certain death on Marye's Heights.
Valor, unit cohesion, and fighting ability weren't concentrated on any one side.
From my reading of many many books, I dont have any reason to believe southern soldiers were particularly better motivated, or better drilled or had better morale.
One key factor to consider (there are many) the south won a lot of battles especially early on. However, many of these were fought on southern territory where they were often on the defensive and very often had the advantage of intelligence as friendly civilians were everywhere.
But look at the results when the southern force essentially swapped roles and went north and on the offensive. South Mountain, Gettysburg, Perryville, Nashville, Franklin. Southern Forces operating in the north and/or on the offensive were no more successful then northern forces. Note the battles I cite, some of them were on southern soil but the south was on the offensive. Also Antietam was in Maryland, neutral state, and Lee was on the defensive.
Having thought about this question for a long time, one could make an excellent case that disparity in results for the north/south was mostly due to the north being on the offensive and operating in hostile territory. Later on as the southern infrastructure collapsed, these factors made it even more difficult on the south.
Another different angle: take a look at the desertions in the southern Army of Tennessee, in the latter stages of the war, that army was carry maybe like 40% troops that were absent in some way or another. This army had retreated a long way, for a long time and had serious leadership issues. They fared probably worse in terms of morale than any union army. Again this has nothing to do with where the troops were from but from the fact they were up against it, they were in retreat they had bad leaders, etc.