The roots of the Fugitive Slave Act included in the Compromise of 1850 can be found in 1793 when Congress first passed the Fugitive Slave Act. In the original law, it was stated that local governments could seize and return any and all escaped slaves, and that those who were found guilty of aiding escaped slaves could be punished accordingly. This law was met with fierce resistance by the people of mostly northern states and because of this it was loosely enforced until the new act was passed. In the mid-1800's, southern politicians started pushing for stricter fugitive laws, and which ultimately led to the inclusion of the Fugitive Slave Act to be included into the Compromise of 1850. The Fugitive Slave Act of 1850 had a profound effect on sectionalism becasue the poeple in hte northern states viewed it as a horrible and attrocious act while the people of the south embraced it.
This new act was much the same as the original except for slight variations. Along with harsher punishments for those who aided slaves and the lack of due process awarded to slaves, the Act also stated that every citizen was required by law to turn in any black man or women suspected of being a runaway. This newest version of an already hated law was met with with even more resistance than the last. Northern free states started passing laws to circumnavigate and even nullify the act. The number of runaways reached an all time high in the mid-1850's as abolitionists doubled their efforts to free the runaways. Violence also broke out in many areas as a result. In one instance in Boston, the people stormed the court house and set free a wrongly convicted black man named Shadrach Minkins. You can read more about this here. And there are countless more stories of abolitionist completely disregarding the law and turning their anger into violence for the sake of their beliefs.
This one most likely the biggest reason why the Fugitive Slave Act was so hated. It forced northerners to make an extremely hard moral decision: Follow the law or follow what they know to be right. The abolitionist resented the law and those who passed it because it forced them into being slave-catchers. For many of them, black men and women had become another part of society. They could read and write and held jobs. For many northerners who weren't particularly passionate about the cause suddenly found this seemingly distant and irrelevant topic in their towns and neighborhoods. They saw the horrors of slavery first hand and the this led many to reproach their stance. The fact that many and most states passed some sort of preventative law to get around the Fugitive Slave Act not only shows the deep resentment for it at all levels, but it also showed that the State had the power to nullify Federal laws; that the individual state held more power. This dramatically increased the sectionalism among U.S. citizens as now huge numbers of people were now blatantly disobeying laws because they felt that they were unjust and this wasn't just a northern state thing. Only a few years after this, South Carolina will demonstrate that the state is more important than the central power when they secede from the Union after they feel misrepresented. In regards to the Fugitive Slave Act, most if not all Southerners were greatly in favor. In its passing, all runaway slaves were required by law to be returned. SLaves were for many people, their entire economic livlely hood so if one slave ran way, the effect was felt. This Act also provided a unique opportunity for southern slave owners that they had not been presented with before. Often times, free black men anad women were accused of being runaways and taken into enslavement, increasing the evergrowing slave market. The fact that states that often times share a boarder could hold such enormously different views on the Fugitive Slave Act goes to show how deeply rooted into each region slavery was.