If the Union was all about freeing slaves then why where there lynchings and segregation? Why could black men not vote or work in skilled trades? Why did they have blatantly racist laws preventing free black people from actually getting rights as citizens? Why did they have the countries most violent race riot?
http://www.pbs.org/wgbh/aia/part4/4p2957.html
"African Americans also faced violence at the hands of white northerners. Individual cases of assault and murder occured throughout the North, as did daily insults and harassment. Between 1820 and 1850, Northern blacks also became the frequent targets of mob violence. Whites looted, tore down, and burned black homes, churches, schools, and meeting halls. They stoned, beat, and sometimes murdered blacks. Philadelphia was the site of the worst and most frequent mob violence. City officials there generally refused to protect African Americans from white mobs and blamed blacks for inciting the violence with their "uppity" behavior."
Doesn't sound like people willing to fight and die to free slaves.