(Another example here would be https://en.m.wikipedia.org/wiki/Aum_Shinrikyo)
If I said "I am going to drop a nuke on jebarker" that's not a credible threat unless I happen to be a nation state.
Now, if I said "I'm going to come to jebarkers house and blast him with a 12 gauge" and I'm from the US, that is a credible threat in most cases due to the ease of which I can get a weapon here.
And this comes down to the point of having a magic machine in which you could ask for the end of the world. The more powerful that machine gets the bigger risk it is for everyone. You ever see those people that snap and start killing everyone around them? Would you want them to have a nuke in that mood? Or a 'lets turn humanity in to grey goo' option?
Our different systems of intelligence keep falling back to ideas of human intelligence and its limitations. Things like we don't multitask well, our best attention is given to one thing at a time. Things like our highest bandwidth senses are our ears and eyes, and even then they are considerably bandwidth constricted. Human limits like our abilities cannot be horizontally scaled in an easily measurable way, and adding more people massively increases the networking costs of accomplishing a goal.
If for some reason the smartest AI can only reach the levels of the smartest human beings (which at least to me makes no sense), then this is still massively powerful, as of this point pesky human problems like 8 hours of sleep are not needed. If human level AI power can be shrunk down to near cellphone size and power consumption, which again doesn't seem out of the realm of physics, lays down the framework for an intelligence explosion at the rate which we can print chips out and assemble them.