We don’t talk about these things, shhh! Administering a brainwashing-enslavement drug en masse is par the course for the series where the protagonist released thousands of murderers and rapists into the world and received absolutely no moral condemnation for it.
Pro tip: if it’s being done for the protagonists’ benefit, it can always be justified, yay!
honestly It's really hard to judge , One Piece world contains intelligent non-human being, hence making it very different to ours. On top of that, moral itself is subjective, there is no absolute objectivity when judging what's right and what's wrong in morality. For instance, you wouldnt be blamed for eating animals, while on the other hand you would get blamed and possibly sentenced to death for eating human despite animal and human are basically the same scientifically
As for Tama taming (or being perceived as slaving according to some people) the gifters, there are more to talk than simply calling it wrong or right. We need contexts involved within the story to comprehend the situation, it's actually roughly the same as making them your allies but with a cheap trick. Sure most of the time we cant judge who's right and who's wrong in a war, but in this context, clearly the faults are on the Beast Pirates, so in this context, Tama wasnt wrong in my opinion.
An analogy would be
Suppose there is A whose family is being murdered by cruel people, then A decided to take 1 of those cruel people as a captive so as to stop them murdering his family, is A justified in your opinion?