1) Animals are still animals, and while we ascribe them human emotions, they are animals, and we must remember that.
That's a very pragmatic, even pessimistic view of the relationship of humanity with domesticated animals. Dogs can go game, even the most tame horse may buck, and cattle, the standard metaphor for "an easily led animal" can stampede. The mindset is "this animal can still be dangerous, and must be controlled". That is the mindset that those running Starship UK want its passengers to have, in case they ever find out about the titular beast.
2) The relationship of the Beast and its passengers is far different from that of a beast of burden, and it is time Starship UK knew that.
The assumption made by the Earthers upon the arrival of the Star Whales was "Oh, how lucky, these dumb animals are passing by just as we need them, let's get them hooked up with a bridle and set up a whip, as we have done with oxen and horses since time immemorial" The Beast and its situation was kept a secret because however necessary the relationship was, people might see it as unnecessarily cruel, hence the forced "choice" between dissension and acceptance. But once the true relationship was discovered, the need for secrecy changed - now the Beast could be seen as a benevolent friend (albeit one treated horribly for decades, maybe centuries) and not, essentially, a slave that needed controlling.