Because when you get down to it, there are two ways an AI can be intelligent. Either it participates in the human world - in which case we are inherently part of its future - or it doesn't - in which case we are irrelevant to it, and it is irrelevant to us, and essentially in exactly the same way as bacteria. Sure, bacteria can kill us and the world is more risky with them in it. And sure, looked at from a certain angle, we evolved "beyond" bacteria and thus took over the world from them.
But when you look at reality, first: we're made of bacteria. And even if you don't consider eukaryotes just a good way for a few bacteria to survive better, there are actual bacteria that live in us, to the point that there are more bacterial cells that make up you than there are human cells with human DNA, and you would die without them.
So even though evolution has gone "beyond" bacteria - it's gone beyond them in a way that in no way makes their lives worse, because it really is bacteria all the way down. So far from being surpassed, actually the bacteria have conquered everything.
Human culture is a software running on that substrate, in a sense. The things that make us human are our language, our ideas - and those are at an entirely different level from the bacterial. They coexist as separate continua, really.
So let's assume that there arises a higher-level self-aware mind (and let's further assume that hasn't happened yet) - at worst it's going to evolve "beyond" us in the same way we are "beyond" the bacteria. I don't see that as precluding us continuing in our mundane human existence in a way that the vast majority of us will never notice.
So to be perfectly clear - I personally believe entirely that something like the Singularity is in our future. What I think is crazy is the idea that we will be superseded. These anti-tech terrorists think it's going to be Terminator, when actually it's going to be something like a more ubiquitous Internet. Nobody's afraid of the Internet - the terrorists aren't, even - even though it's highly probable that the Internet itself is what will evolve into the next level of life.
I just don't see how anybody can look at the changes that are coming down the pike and think, "Oh my God, the future is scary" - it's just going to be better. I mean, shit, I grew up in the middle of nowhere with interlibrary loan the best way for me to find out the really hard stuff. The Internet is like crack to me. I now do programming and technical translation for customers all over the world, and I can move whenever I want. That lifestyle was impossible twenty years ago. Impossible. No agency would track me down by mail if I had to keep leaving forwarding addresses, but now? I go to Hungary for the summer, we lived in Puerto Rico for two years, now I bought a foreclosure close to home (that I found on an Internet search) and we've been here a couple of years - and next year it's back to Europe. My customers might notice I'm getting up six hours earlier, but otherwise it's all the same to them.
As technology gets smarter, I will continue to build it into my life, and as a result, my life will continue to be closer to what it ought to be. I just don't see the downside to that. And as it gets really smart, it's going to be inside my brain anyway, and - poof! Exponential curve. I expect to be part of it. How could it be otherwise?
So, no. I think the only reason to be afraid of the future is if you want to be afraid of something. And I consider that truly crazy.