Slaves were property. The cost money to purchase and maintain. It the slaves used the underground railway, then the owners were out that amount of money and that amount of work the slaves performed.
It didn't make white Supremacy any easier. They had to pay to get the slaves back, so that was another cost.
It was a threat. I can't help the wording of this. Just because this event can be described doesn't mean it was right.
They traveled mainly on foot and did not have the proper footwear. Runaway slaves carried little to no food, and would become weak. Injury and illness was a danger on the Underground Railroad, as well as wild animals. Despite such risks and dangers, the journeys were braved by fugitives to escape from a life Slavery. So a threat.
