Eh, tell that to any Science Ficton story that subscribes to "don't step on a butterfly".
You're not thinking about this straight. Suppose a butterfly landed on your nose in a moment. Now, I imagine that you probably would not kill it, if you could resist reflect impulse, but you would not do so for some irrational fear that your destruction of one insect would destroy future civilizations. And yet, we must grant that it is possible that killing a butterfly in the present could have the same effect on some far of future as some far past butterfly might have on our present.
So why wouldn't you worry about killing a butterfly today?
Well, for one, you're already here, so killing the butterfly would not retroactively end the world as you know it. For another, although such impacts are possible, they are highly implausible, and impossible to know. Indeed, maybe NOT killing the butterfly, or not buying an Ipad, or not ordering a bacon double cheeseburger would have the same effect on some poor future civilization. Your epistemic vantage point is so weak that you have no grounds to kill an insect or save an insect solely on the grounds of concerns for far off future civilizations.
You should recall that the nu-Trek universe is a tangent universe. There is no future to destroy here and the future it would have had has been radically altered by Nero.
Spock, if he is logical, must consider that giving or withholding his knowledge could have grave impacts, and he should do a risk analysis to best determine which alternate future facts to share with the UFP.
Not sharing anything via the butterfly principle, however, is irrationally conservative and neglects the fact that not sharing is also an act. Now given that Spock know that bad things will happen to Deneva if he doesn't speak up (i.e., the whole colony will be wiped out) and tell them to protect themselves with UV light. He has a known HORRIBLE negative outcome involved with NOT acting, and no information about would happen if he helps out. Indeed, his only concern with acting can be "unforseen future ramifications" of the variety that all our acts have. The only logical course of action for Spock is to warn Deneva.
This is not only ridiculous, but morally repugnant.
The odds are pretty even, if you cure a plague, that one of those who died in the time line, lives in this timeline and grows up to become he next Hitler and is personaly responsible for the death of just as many millions as were saved by curing the plague.
It is, in fact, shameful. By your reasoning, we should not cure treatable diseases today
, because hey, it's even money that the next Hitler will die prematurely if we do nothing.
If we really thought this way, we would simply assume that all future consequences are equal and simply do nothing to help other human beings.
We have to look no further than Edith Keeler herself, it was a good honorable, noble thing, and dfinitely the right thing to do to save her life, but, look what she went on to cause when she wasn't killed. So, I assume you believe City on the Edge of Forever is a weak episode, since it is TOS and uses the very same argument?
You couldn't have it more wrong.
The Edith Keeler argument counts in my favor. They have knowledge of what will happen if she does not die. It is because they have certain knowledge that they are compelled to act. Certain knowledge means you are bound to act.
In this case they know what will happen in either case (letting her live or die), so the only tension has to do with the moral problem of suffering an innocent.
Spock has solid knowledge of BAD things that will certainly happen if he does not act, so he is bound to share at least some of his knowledge. On the other side, there are mere butterfly possibilities that would prevent him from doing this. The weight of the impact combined with the certainty of it happening as opposed to the unknown weight of non-action with unknown, means that he acts. For all I know, walking to work today will someday cause a war on Mars, but I don't sweat that mystery detail because I know that if I don't go to work, I will most certainly be fired.