Let’s not pretend that religious stewardship of any state has ever not resulted in human rights abuses. The idea of a caliphate in Germany should rightly horrify the German people. Fundamentalist Islam (or Christianity) can easily cite scripture to justify child brides, executions, and domestic violence.
So let’s flip the question; why aren’t you horrified at the idea of a caliphate in Germany, and seemingly hand waving the atrocious results it would bring?
I highly recommend Stephen Tetlock’s book, super forecasting, who is the sponsor of the project you mention.
One method of forecasting that he identified as effective was using a spreadsheet to record events that might occur over the next 6-18 months along with an initial probability based on good judgement and the factors you quoted. Then, every day look for new information that adjusts the forecast up or down by some, usually small percent. Repeat, and the goal is you will trend towards a reasonable %. I omitted many details but that was the jist.
Now, that’s for forecasting on a short ish timeframe. There is a place for more open ended reasoning and imagination, but you have to be careful not to fall prey to your own biases.
This particular forecast of OPs feels like it is ignoring several long running trends in technology adoption and user behavior without giving events that would address them, and forecasts something they care about doing better in the long-term, a source of bias to watch. I tend to agree with you that I think elements of this forecast are flawed.