I have a few thoughts about doomsday level AIs:
1. We _will_ eventually crack "general intelligence". If nature is able to do it with 9 months of build time and a few pounds of meat, there's no physical reason we can't do it on silicon (or whatever substrate is next)...
2. When we finally develop a half-way decent general intelligence, much like human intelligence, we're not going to have any idea how it works.
3. It will probably end up employing a lot of the same cognitive shortcuts that humans use (see https://en.wikipedia.org/wiki/List_of_cognitive_biases). And in doing so we're likely to end up with a general intelligence that, on the whole, is capable of much greater calculation, but ultimately will be a disaster as it will suffer from the same sort of psychological flaws.
Human survival is probably going to come down to humanity trying to talk a super-intelligent AI out of some crazy ass conspiracy theories. It will be like the ultimate Thanksgiving with your crazy uncle.