OK, I am convinced now! The post from Brian Abraham above shows quite clearly how a forward speed increase at sea level directly and signifcantly reduces net thrust, which concurs with the principle that exhaust speed cannot be less than forward speed. So I am happy to admit I have learned something, which in retrospect I should have been able to figure out.
Thank you to those posters who so patiently took the trouble to explain it and to those who were able to resist the temptation to be condescending.
Most importantly, I thank the original poster for initiating the discussion and I hope he/she enjoyed the postings.