Bigotry is wrong, but it isn't always irrational. In this case we're discussing soldiers who saw their comrades die at the hands of soldiers of another race or culture. In cases like this, it is entirely rational for these folks to harbor negative feelings for Japanese, Germans, or whomever the enemy was. What makes it wrong is their tendency to aggregate all members of that race or culture and throughout time, thereby including more who aren't or weren't the enemy than were.