"First, the existential threat [of AGI] may be low."

Let me trace back the argument tree for a second. I originally asked for a defense of the claim that "SIAI is tackling the world's most important task." Michael Porter responded, "The real question is, do you even believe that unfriendly AI is a threat to the human race, and if so, is there anyone else tackling the problem in even a semi-competent way?" So NOW in this argument tree, we're assuming that unfriendly AI IS an existential threat, enough that preventing it is the "world's most important task."

Now in this branch of the argument, I assumed (but did not state) the following: If unfriendly AI is an existential threat, friendly AI is an existential threat, as long as there is some chance of it being modified into unfriendly AI. Furthermore, I assert that it's a naive notion that any organization could protect friendly AI from being subverted.