I hope you don't mind if I weigh in?
I'm afraid that you've encountered one of the many emotionally stunted people who take refuge in academia. I'm sure your undergrad prof. is a fantastic thinker, researcher, teacher and all the rest of it. But many, many people stay at school for the shelter it provides, as much as for the intellectual opportunities it offers. It can be a bubble, and the bubble can preserve people in amber, emotionally. This man is one such case, I'd stake my life on it.
He was disappointed that your mutual efforts would come to nothing, and he reacted like a child. It was unprofessional and unneccessary, even if he means the best for you.
My only advice is that you should not allow him to infect you with his irrationalism. A PhD at Cornell would be a remarkable achievement and I think you must pursue it. Then go back to this guy in five or six years and tell him all about your real 'achievements of distinction'.