An over-simplification, but an evocative one:
- The social sciences are contentious, their predictions questionable.
- And yet social sciences use the scientific method; AI predictions generally don't.
- Hence predictions involving human-level AI should be treated as less certain than any prediction in the social sciences.
That implicitly assumes that there aren't reasons why social sciences are contentious which don't also apply to AI predictions, but I don't think that's terribly unreasonable (EDIT: where by “I don't think that's terribly unreasonable” I mean that the reasons why the social sciences are contentious despite using the scientific method that I can think off the top of my head would also kind-of apply to AI predictions).