One thing that I can think of is that the "Good" Generals were more personalable and not so removed from their men. Those Generals were more like old home boys, than they were demigods.
Viet Nam is really not a good comparison, because we didn't know why we were there, even today, except that the government drafted us and sent us. In the Civil War there were two reason why the early volunteers fought. For the South it was "Independence". In the North it was to "Preserve the Union". Both are noble causes, even today, and are the only ones which might justify the great sacrifics which were made. But, once the fever of those "causes" died down, and the political agendas were introduced, the reasons for continuing the fight became less clear to the common soldiiers on both sides.
I could see myself marching off to war for Independence, or to preserve the unity of my country. I would fight to preserve the Constitution. But to go to war to preserve slavery, or free people from slavery who I do not know, would be something that I would probably not do without being drafted.