I agree with Invo. At one point Taravangian tells Dalinar that the half-shard fabrials use spren that once helped Radiants, strongly hinting that they have trapped sentient spren, so I'd argue that things like half-shards are not humane, but fabrials that have trapped things like flame spren are, as it is more similar to using a chull to pull a wagon than having a human slave.