Science can be used to show how material entities react to events. The optimism comes in assuming that this is sufficient to explain the occurrence of every event which has ever happened.
To illustrate simply, science can correctly predict how a moving billiard ball will react with the other balls on a table, but it can't be used to define the ultimate cause for the trajectory of the moving ball. Optimism comes in the assumption that the ultimate case is just a chain of scientifically defined cause and effect events tracing back to the big bang with no outside interaction. If outside interaction is used to explain the cause, then this must come from an event which was induced outside the physical cause and effect chain.
To take your last statement which I accept started with an'if' but does that mean normal human curiosity is now forbidden? Shouldn't we be allowed to ask such questions as:
Where does this event come from?
How does this event react to and influence the progression of cause and effect?
Where is the evidence for such an event?
Can this event be described in detail?
Is there any reason to think that this event actually exists/existed?
Of course, if you respond to this by suggesting that God is, or is instrumental in producing, this event, then exactly the same questions should surely be allowed by simply substituting the word 'god' for 'event'. I would suggest no positive progress has been made in answering such questions.
Of course, you may respond by suggesting that we don't know the answers to these questions. I would have no problem with that at all. After all, we can ask exactly the same questions about the big bang. However, in science, much positive progress has been made in response to such questions.
Perhaps, on reflection, you actually mean 'postive' rather than 'optimistic' when you seek to describe science based theories.