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.
The social sciences are sciences; AI predictions are mainly speculative thinking by people who just put on their thinking caps and think really really hard about the future (see some of the examples in http://lesswrong.com/lw/e79/ai_timeline_prediction_data/).
Are you saying that these predictions are unscientific because they are based on untestable models? Or because the models are testable for "small" predictions, but the AI predictions based on them are wild extrapolations beyond the models' validity?