Complex sentence: Abolitionism generally opposes movements that seek to make animal use more humane, since they believe this undermines the movement to abolish animal use, and also generally oppose campaigns to abolish specific forms of animal use, since they believe this undermines the movement to abolish all forms.
Split into simpler sentences: Abolitionism generally opposes movements that seek to make animal use more humane, since they believe this undermines the movement to abolish animal use. Abolitionist also generally oppose campaigns to abolish specific forms of animal use, since they believe this undermines the movement to abolish all forms.