lol ^
the Superhappies, for all their advancement, didn't seem to think things through. There is the fact that we develop from adversity, which is why their solution is wrong (what concept of individual liberty do they have? Obviously some given their reaction to the Babyeaters). There is the fact that our suffering inflicts suffering upon them through empathy. The simple solution there is to not communicate, or to communicate solely through simple text media.
I AM SUPER HAPPY FUN BALL I WILL SPEAK IN METAPHOR
Imagine that the man who lives next door to you tortures a kitten every day. He came from a country where they used to have to torture thirty kittens every day, mind, so torturing only one is an improvement. His society has written reams of poetry and beautiful art about the sad and painful necessity of torturing kittens. It is part of their soul.
But nonetheless, although he doesn't have to torture the kitten any more - he can take medication to prevent it - he explains that circumstances conspire to make it happen every day, and that it is simply part of his identity.
Now, you don't have to ever see this man, and you can't really hear the yowls of his kitten. But now that you've met him, and read all his books, you know he's over there, torturing that kitten. And you really could force him to take his medication...
That's how the Superhappies feel about humanity, only more so. Is cutting off all contact somehow a solution? Does the man have a cultural right to torture his kitten?
Been mulling over this, and did a very illuminating wiki walk on various points of view on ethics. (I'm still not an authority on this at any rate

)
I stand by my initial reaction that humanity feeling suffering is not at all like the torture of a kitten. An individual wronging another individual is almost always ethically wrong, but the cumulative suffering of humanity is an abstract concept. It's not universally wrong or right, it's what we get out of it. We may or may not benefit from a wider "emotional spectrum", as IronBeer puts it, but we definitely learn from adversity. All in all, the ability to feel suffering is a positive aspect of humanity (in a post-scarcity society this might be debatable but the Humanity in the story is very likely not post-scarcity).
Because of our basic psychology, taking away that aspect would be to our detriment in one way or another. For the SH's, their psychology seems to lend itself to a "happy-happy-joy-joy" existence, and it is a positive factor for them. Thus in both cases, what we have now is what is right for our society from an objective standpoint.
The only remaining point of conflict is the SH's perfect empathy. Now, memories can be passed down into what is basically a collective consciousness for them. Either this cultural memory is perfect or it is not.
The unlikely case first: if it is, any suffering is spread throughout their society like a virus. The effect may diminish as it is shared, but it is always there. They know about humanity's suffering and it causes them pain, which they share with all their species. This suffering, for them, is there whether or not they "cure" us. They have already been damaged, and much less so than by the knowledge of the Babyeaters culling their young (remember, that revelation basically incapacitated their captain). They can leave us in peace and not be much worse for it.
The likely case: memories are not transmitted perfectly, they are forgotten and die off in the cultural memory. If this is true, the damage we would do by letting them know we suffer is finite. If they can keep secrets, they could in fact let the memory die with their crew and close families. In this case, the finite damage we do to them is far, far less than the irreversible damage they do to us.
[EDIT] Ghostavo: um
noBoth defect: both get a 5-year sentence.
Both cooperate: both get a 6-month sentence for a minor charge.
One defects: defector goes free, other gets full 10-year sentence.