The weakest argument against AI was the standard: Free will (or creativity) hence no AI!
I am most appalled by "philosophical externalism about mental content, therefore no AI." Another silly one is "humans can be produced for free with unskilled labor, so AGI will never be cost-effective."
The weakest argument in favour of AI was the perenial: Moore's Law hence AI!
On the other hand, imagine that computer hardware was stagnant at 1970s levels. It would be pretty plausible that the most efficient algorithms for human-level AI we could find would just be too computationally demanding to experiment with or make practical use of. Hardware on its own isn't sufficient, but it's certainly important for the plausibility of human-level AI when we find performance on so many problems scales with hardware, and our only existence proof of human-level intelligence has high hardware demands..
Also, you occasionally see weak arguments for human-level AI by people who are especially interested in some particular narrow AI field, which reaches superhuman performance, that assume the difficulty of that field is highly representative of all the remaining problems in AI.
..."humans can be produced for free with unskilled labor, so AGI will never be cost-effective".
Not only is this argument inductively weak, the premise seems obviously false, since childcare is actually quite expensive.
While going through the list of arguments for why to expect human level AI to happen or be impossible I was stuck by the same tremendously weak arguments that kept on coming up again and again. The weakest argument in favour of AI was the perenial:
Lest you think I'm exaggerating how weakly the argument was used, here are some random quotes:
At least Moravec gives a glance towards software, even though it is merely to say that software "keeps pace" with hardware. What is the common scale for hardware and software that he seems to be using? I'd like to put Starcraft II, Excel 2003 and Cygwin on a hardware scale - do these correspond to Penitums, Ataris, and Colossus? I'm not particularly ripping into Moravec, but if you realise that software is important, then you should attempt to model software progress!
But very rarely do any of these predictors try and show why having computers with say, the memory capacity or the FOPS of a human brain, will suddenly cause an AI to emerge.
The weakest argument against AI was the standard:
Some of the more sophisticated go "Gödel, hence no AI!". If the crux of your whole argument is that only humans can do X, then you need to show that only humans can do X - not assert it and spend the rest of your paper talking in great details about other things.