Answer:
They were infuriated by this law.
Step-by-step explanation:
The reasons that African Americans and many others were so upset about the passage of this law was simple. For one any slave that escaped the treacherous grip of slavery was now at risk of being sent back. Secondly this put free blacks at risk of being captured and put back into slavery in spite of already earning their freedom. Finally it made all escaping slaves need to escape into Canada as opposed to northern states that were much closer.