Sending people as a human right violation that they saw breaking the rules set by declaration of independence. Yes the underground railroad was breaking constitutional habeas corpus rules but they were also breaking rules of common man.
Agin may be wrong but i remember that the north used this as the justification for harboring fugitives. This doesnt hold for this case , though, as its breaking interstate ex post facto laws. Its also breaking full faith and credit as stipulated by article IV in the constitution.