My Druid is a member of Liberty's Edge, his belief is that nature should be free or or if it must be bound by work in a mutually beneficial labor relationship (example, the cart horse pulls the cart but gets food and shelter and is taken care of, so both sides are better off for it)
Slavery is only beneficial to the slaver and not the slave.
Since all things share a part of the natural balance all things should be free and since slavery is against that balance it must be destroyed so the balance is maintained.
That is why my druid is a Pathfinder