Why would the US congress pass such laws to return slaves who escaped back to their masters?

The Act was one of the most controversial elements of the 1850 compromise and heightened Northern fears of a "slave power conspiracy". It required that all escaped slaves, upon capture, be returned to their masters and that officials and citizens of free states had to cooperate.

a goverment for the people by the people

the articles of confederation only set up the continental congress at the federal level. there were no executive or judicial branches except within the states. the states were allowed to keep every right that was not specifically given to congress. the bonding of the states was through a 'firm league of friendship' that best served as a defense agreement against invasion. states were not allowed to use taxes as a way to discourage treaties, and states were extremely limited in their dealings with foreign nations.

not many historians today talk about the strengths of the articles of confederation, likely because of how unpopular the document quickly became. the articles did set the legislative body, congress, as the highest power in the nation because of the fear of monarchy. congress had the sole power to declare war, assign treaties, entertain foreign relations, and operate post offices. disputes between states and territorial issues were to be brought to congress. the document also stipulated that canada was allowed to enter the union if they desired.

there were more weaknesses than strengths under the articles of confederation. the lack of power given to the continental congress strangled the federal government. the articles gave congress the power to pass laws but no power to enforce those laws. if a state did not support a federal law, that state could simply ignore it. congress had no power to levy taxes or regulate trade. without a federal court system or executive leader, there would be no way to enforce these laws, either. amending the articles of confederation would also require a unanimous decision, which would be extremely difficult.