What's wrong with having a bunch of 'slaves' in our people's possession? It would give our people time to be thinkers and students, more capable tacticians and engineers and whatnot.
Besides, we don't have to have the modified troglodytes treated terribly. And in fact shouldn't. Even if we turn them into bug people they're probably still more than capable of murder.
But alright, if we've got problems on ethics and how intelligent they are, perhaps we could ask the knowledge goddess how they differ; we looking at fully-developed mental beings, or upright animals?
Okay, sure, calling them slaves may be a bit much, but they wouldn't be indentured servants nor cattle. I just propose a class of workers to handle the menial tasks in our society. Creatures with less free will fit this description perfectly. Perhaps, in order to shrug off any abuse, we assign them the rank of 'public service'?
Remember that the soul is a measure of free will, too. They have less of it than humans. But enough we can expect them to take initiative instead of being mindless.
Hmm, considering this, it may be wise to convert to communism(or something like that(don't pretend we're not a despot already)) if we use a worker class, considering what it would do for our internal economy. Though, granting people animals to produce trade goods for their own wealth would be a wise idea.