For me, the futility of GOFAI is obvious from simple introspection: is my own brain capable of chaining through vast networks of propositional statements? I wish! I can barely hold a 5 node decision tree in my head while playing a board game. At the same time, my brain is amazingly good at parsing visual and linguistic stimuli.
Still, you have to respect the man's dedication to his quixotic quest.
Yeah but helicopters fly. The problem with cyc is that it never really got off the ground.
Symbolic AI wasn't a failure but it never really worked for any problem space without rigid rules you could define and that's with some of the greatest minds trying for decades to make it happen.
At this point real-world intelligent symbolic AI only exists in fiction and our collective imaginations. Technically, no one has proven it can't work, but at some point you have to face the reality.
Still, you have to respect the man's dedication to his quixotic quest.