They have to believe their cause was just, or it means they were the agressors fighting against self-government.
Hmmmmm ... (thoughtful pause) ... I think some people just get a bug up their b*tt, one way or another. The local SCV chapter here won't display the United States flag because they say "You can't serve two masters." A bit loopy, IMO, and not the sort we want teaching history to our Cub Scouts.
However we wish things might have turned out, past is past.