See, that's what I can't understand - why do people (not just on the DIS but on the other Lost forum I read) believe that "whatever happens, happens" is the gospel truth, written in stone, total fact? Just because Daniel said it, doesn't mean it's true. Can't Daniel be wrong about something? Look at the girl who's stuck in a coma (can't remember her name right now) - we've pretty much assumed that she's one of Daniel's experiments that didn't quite work. Daniel was wrong about something; why can't he be wrong about "whatever happened, happened"??
And don't forget - Daniel was on Widmore's freighter, his research was bankrolled by Widmore, and Daniel's mother (Eloise) was working for Ben (and her whereabouts known by Widmore, so maybe she's working both sides). Just because Daniel is the typical scatter-brained scientist doesn't mean that HE might be trying to manipulate people, too.
I think you'd be surprised how many don't buy that theory. Right now I do beleive that is where the writers are coming from but a lot do not believe that so you are not alone.
For me, it does not just stem from Daniel. But also other things that we have seen happen. Ethan for example. If the losties hadn't saved Amy he would not have been born and we know he was alive and well on the island in 2004.
Also, Eloise in talking to Des said that the universe tends to course correct and she used the illustration of the man in the red shoes. If she had saved him then he would have died another way. Same way with Des saving Charlie.
Also, if Sayid did indeed kill Ben then it would have unraveled the whole Lost story. Ben is what brought them all back so if he died at the tender age of 12 then he wouldn't have been around in 2007 to bring them all back to the island and thus Sayid wouldn't have been on the island to kill him.
I don't think I am doing a very good job of explaining. It makes a lot of sense in my head right now. But all of that could change if the writers give us a twist in the next couple episodes.