By the fact that Henry came up with the idea of calling certain people rhinoceroses, we know that neither Bernard nor Helmholtz are unique. They're not all that common in the Fordly society, but they've got common precedent. (That helps to make them a good analogy for similar cases in today's world or one contemporary to Huxley.)

This suggests that there are limits to what the conditioning can accomplish. Sure, with enough repetition, you can get somebody to react to your words as though their own thoughts. But, the fact of Bernard means that conditions in the world can counter the conditioning.

I would hasten to add that it's likely impossible for the Fordly Society to provide anybody with a life free of such counter-conditioning conditions.

So, there would be some necessity.

Also, it's worthy of note that this wouldn't necessarily be a conscious choice. People naturally draw up uncharitable images of their ideological opposition and treat that as the alternative to their own way of thinking.

That's how "feminism" becomes "man-hating". That's how a focus on consent becomes "anything goes so long as there's consent". So, in one part, Fordly society might be using the Savage Reservations just to make themselves feel better about where they are.