Something that is important to understand about the northern United States at the time Huck Finn is set, was that most northerners were not abolitionists. They didn't want to see the influx of people just as much as the southerners didn't want to lose their free labor.
However, there were significantly more abolitionists in the north than in the south. Many key abolitionists were slaves who had escaped to the north like Frederick Douglass. Others were forward thinking white people who thought slavery was wrong and wanted to see equality. One of these people was Charles W. Chestutt. He presented a view of African-American slaves in a different light than Hentz. His piece, "The Passing of Grandison" highlights the differences in thinking between white southerners and white northerners in the United States prior to the Civil War.