Well it might make perfect sense from their perspective, there might be a million alien species on the galactic council who all agree they don’t want to deal with a species that won’t purge at least one race.

It’s unlikely but possible, we have literally no way of knowing or really guessing anything about how an alien race or empire might think. They might be shocked and confused we don’t kill our enemies children, bemused that we ended slavery, disgusted that we don’t torture criminals for sport…

An even scarier thought is that we might agree with them in a hundred or thousand years, it seems impossible to imagine but to me it seems impossible to imagine slavery was ever a thing or that they put criminals heads on pikes for everyone to see.