My evil side makes me wonder what myths we have today that will be de-bunked in 100 years. :)
In almost any field, you can find old mandarins struggling manfully to suppress the work of youngsters who will overturn their fond delusions as soon as they have retired or died. The former group, emeritus with plenty of free time, are all over Wikipedia defending their legacy against appalling new evidence.
There is even a law, attributed to Max Planck: "Science advances one funeral at a time."