Well "is able to e.g. cure cancer" is not actually very general. Which leads to the problem with 2) whats the economics behind creating a general intelligence when a specific intelligence will get you better results in a given industry. Even then specific intelligence is still going to be subject to the good-enough economic plateau that has killed so many future predictions.
Then the problems with 4 on up really concern the speed with which 4 can feasibly happen. The AI goes FOOM doomsaysers seem to think that we'll end up with an AI which is so horribly inefficient that/and it will be able to rewrite it self to be super duper intelligent without leaving its machine (and won't accidentally nerf itself in the attempt) and then that super duper intelligent computer will trick several industries into building an even more powerful body for itself etc... all of this happening before humans pull the plug. no step of which is has anything beyond speculation to support it.
In a general note the full employment theorems mean that even if general AI is economically incentivized there's still going to be dozens/hundred/thousands of different AIs carving out niches for themselves which, given that the earth/universe has limited resources, handily prevents the paper clip maximizer problem. While the future may not need humans it will still be a diverse future.
Then the problems with 4 on up really concern the speed with which 4 can feasibly happen. The AI goes FOOM doomsaysers seem to think that we'll end up with an AI which is so horribly inefficient that/and it will be able to rewrite it self to be super duper intelligent without leaving its machine (and won't accidentally nerf itself in the attempt) and then that super duper intelligent computer will trick several industries into building an even more powerful body for itself etc... all of this happening before humans pull the plug. no step of which is has anything beyond speculation to support it.
In a general note the full employment theorems mean that even if general AI is economically incentivized there's still going to be dozens/hundred/thousands of different AIs carving out niches for themselves which, given that the earth/universe has limited resources, handily prevents the paper clip maximizer problem. While the future may not need humans it will still be a diverse future.