Apparently I don't understand what you mean by "serious risk". (Before I pick this apart, by the way, I agree that we should try not to Godwin people -- because I think it doesn't work.)
I consider it likely that AGI will take a long time to develop. A rational species would likely figure out the flaw and take corrective steps by then. But look around you. Nearly all of us seem to agree, if you look at what we actually want according to our actions, that we should try to prevent an asteroid strike that might destroy humanity. As far as I can tell we haven't started yet. No doubt you can think of other examples: the evidence says that if we put off FAI theory 'until we need it', we could easily put it off longer than that.
[...] SIAI's Scary Idea goes way beyond the mere statement that there are risks as well as benefits associated with advanced AGI, and that AGI is a potential existential risk.
[...] Although an intense interest in rationalism is one of the hallmarks of the SIAI community, still I have not yet seen a clear logical argument for the Scary Idea laid out anywhere. (If I'm wrong, please send me the link, and I'll revise this post accordingly. Be aware that I've already at least skimmed everything Eliezer Yudkowsky has written on related topics.)
So if one wants a clear argument for the Scary Idea, one basically has to construct it oneself.
[...] If you put the above points all together, you come up with a heuristic argument for the Scary Idea. Roughly, the argument goes something like: If someone builds an advanced AGI without a provably Friendly architecture, probably it will have a hard takeoff, and then probably this will lead to a superhuman AGI system with an architecture drawn from the vast majority of mind-architectures that are not sufficiently harmonious with the complex, fragile human value system to make humans happy and keep humans around.
The line of argument makes sense, if you accept the premises.
But, I don't.
Ben Goertzel: The Singularity Institute's Scary Idea (and Why I Don't Buy It), October 29 2010. Thanks to XiXiDu for the pointer.