Why did the southerners feel the way they did about the Fugitive slave law?

The fugitive slave law gave southerners some protection against being bankrupted by thousands of escaping slaves. The law gave northern banks greater willingness to support slavery by loaning money to slave owners. The law also had the effect of co-opting the support of northern newspapers, which carried the very profitable ads for return of escaped slaves. Basically, the fugitive slave act gave national endorsement to the whole system of slavery.