(First I disagree with A Secular Age's thesis that secularism is a new force. Christian and Muslim churches were jailing and killing nonbelievers from the beginning. People weren't dumber than we are today, all the absurdity and self-serving hypocrisy that turns a lot of people off to authoritarian religion were as evident to them as they are to us.)
The idea is not that AI is on a pre-planned path, it's just that technological progress will continue, and from our vantage point today predicting improving AI is a no brainer. Technology has been accelerating since the invention of fire. Invention is a positive feedback loop where previous inventions enable new inventions at an accelerating pace. Even when large civilizations of the past collapsed and libraries of knowledge were lost and we entered dark ages human ingenuity did not rest and eventually the feedback loop started up again. It's just not stoppable. I highly recommend Scott Alexander's essay Meditations On Moloch on why tech will always move forward, even when the results are disastrous to humans.