This whole argument is total bunk. The basic premise is that progress has been very fast till now, so it'll continue.
If you take something like powered flight, we went from a basic engine and propeller on a balsa wood frame at the turn of the last century to 400mph fighters by the 1940s. We then went to 3000mph jets screaming around in by the 1960s, and by the 1970s we had rockets travelling 15,000mph to the moon! Given this astonishing rate of progress, clearly if you add on another 50 years, we'd be travelling to other planets in the solar system, or maybe to the other side of our galaxy by now, right? Ha.