To the best of my knowledge, most groups of Humans on Earth have at some point had slavery as a part of their society. Do you believe otherwise? Would you apply your 'kill 'em all' belief to Ancient Rome, or Greece, or to the Middle Eastern of the 9th-11th centuries? Because they all had slaves. Britain had slaves for a long time before phasing it out during the 11th century in favour of serfdom, and I'm sure that we all know how recently the United States had it. Heck, most of the
Founding Fathers personally owned slaves.
I mean, the big issue with bringing in Greece and Rome is that their form of slavery was radically different from what we're seeing here and what went down in the American South. Greco-Roman slavery, for one thing, had laws about how a slave could be treated - you couldn't legally beat or otherwise physically punish a slave without providing due cause, you couldn't kill a slave you owned unless there was evidence they had committed major crimes (rape/murder kind of major) - and most significantly, it was not uncommon for city slaves (and even field slaves) to be freed by their masters, to the point where a cornerstone of how Roman business worked was that there'd be a circle of ex-slaves who worked as employees and business partners to their former owner, which helped encourage a basic level of decency in many slave owners & helped their society as a whole view slaves as being low-ranking servants or "people-in-waiting" than nonsapient possessions. Likewise, while slaves were technically not allowed to own property or be married, those laws were often ignored in practice, and widespread use of slaves as actors, singers, musicians, clothing-makers, gladiators, and other such positions meant that slaves regularly became celebrities.
There were definitely
issues with the system, mind: slaves who were sent to work in mines or quarries often endured gulag-like conditions (because it was often seen as a way to dispose of "savages", criminals, and other groups who were considered to either deserve such treatment or have already fallen through the cracks of societal empathy), the actual punishments for beating or killing a slave were far from equal with those for beating or killing a freeman, and abuse of various kinds could and did happen that might have been halted or at least ameliorated by the lack of slavery.
However, it was nothing like what appears to be going down here on Tamaran. The Gordanians deny the Tamaranians anything beyond Dark Ages technology, actively seek to destroy their culture and all attempts to retain any since of social unity, & respond with mass killings via orbital bombardment if they
think they're being disobeyed, all while demanding yearly payments for the privilege of not being exterminated completely. Gordanian "hunting parties" routinely descend on a random area of the planet to kill the locals for sport or take them offworld for unknown purposes.
That is a level of casual sadism and sociopathic disregard that honestly exceeds the Deep South, repulsive as the slavery practices there were. The only human civilization I'm aware of that even approached that were the ancient Spartans: their slaves, referred to as
helots, were treated as less than animals. Spartan laws included a mandatory minimum of yearly abuse slaveowners were expected to dispense to their
helots, and a common game played by rambunctious Spartan teenagers was to slip into the helots' sleeping quarters at night and compete to see who could kill the most before the other helots noticed and woke the others.
The Spartans, for reference, were considered vicious, brutal, and more than a bit mad by their contemporaries, who regularly murdered their own infant children if they happened to be deformed or sickly. Instances of helots in a region rising up, invariably because of how poorly they were treated and how much hatred the Spartans engendered in them, were one of the greatest problems the Spartan nation had to deal with (which, by the way is why they instituted mandatory beatings for all helots, in the belief that keeping in semi-constant pain
on top of being overworked & underfed would leave them too drained to revolt), and they happened
very frequently right up until the entire culture's collapse.
At this point, trying to negotiate with the Gordanians will constitute, at best, purchasing the Tamaranians and their homeworld from the clan that currently claims ownership of it. While certainly possible, it still means handing the Gordanians, a race that has done nothing to merit such benevolence, a giant chunk of resources and waving merrily as they sail off into the sunset with their reward for committing recreational murder, cultural genocide, and Hell knows what other atrocities to these people. Anything else (barring just telling them to submit or die, which will then necessitate one or more object lessons) is likely to result in the Gordanians either telling him to fuck off or trying to kill him, and in either case they now know to initiate a fresh round of purges among the local Tamaranian population and be on guard for spaceborne attackers.
OL's disturbing fixation with trying to "civilize" the degenerate warlords, slaver-kings, tinpot dictators, war-criminals-for-hire, and general psychopath Pick'N'Mix of the Vega Systems (even though there is no real reason to believe that such endeavors will or could ever succeed without implanting bombs in all involved parties' heads or otherwise forcing them to reform under threat of death), to the point where he intends to destroy the only group of natives willing to try and make Vega a less horrible place because he considers them "too disruptive", was already nauseating enough. However, doing
that, and then claiming his morals won't permit the swift removal of a group whose actions here make the Nazis look restrained? That is
fucking disgusting, not least of which because it gives the impression that Paul either prioritizes the rights of oppressors and murderers over those of their victims, or that his senses of empathy & ethics are entirely unimportant compared to his desire to prove that he can "win" via means he views as more challenging or more enlightened than more direct, traditional, and morally-motivated ways of handling things.