What was the fugitive slave act and why was it so controversial?

"The fugitive Slave Act of 1850 required all citizens to help catch runaways. Anyone who aided a fugitive could be fined or imprisioned. People in the south believed the law would force northerners to reconize the rights of southerns. Instead, enforcement of the law led to mounting anger in the north, convincing more people of the evils of slavery." The American Journey__________ Zoe Joy Stehlin is a boss don't forget it punks :D <3