The abolitionists objected to slavery for ethical / human reasons.
It can be said that the set of ideas and actions that aims at the extinction of slavery is called abolitionism. In the case of the USA, the abolitionist movement gained strength and importance in the North of the country, a region that was in full economic development and opted for free labor, while in the South the idea of white supremacy prevailed and the ambition to maintain the economic model.
The northern states then supported the election of a laborer, Abraham Lincoln, to the US president, who was elected and immediately instituted a program to limit slavery.
The issues that influenced the abolucionistas were human perceptions that slavery was an atrocity against people and that it was completely unethical and cruel.