Do not all sports carry a small risk of injury?
What is the number of ex-footballers who have had this health issue? - to calculate the risk, you would need this figure and measure it against the total number of ex-footballers, I don’t know the figures but would think it is quite unlikely there is a high risk.

Punching someone in the head ie; boxing, should this be banned? - far greater risk I would imagine.

All marshal-arts sports carry a risk of long-term injury as does cricket, cycle racing, motor sports, horse-riding - it is noticeable that many of the sports I have mentioned (boxing apart) mostly wear some form of protective headwear but in football, I believe it will have to be a personal choice if and when protective headwear becomes available.

If you don’t want fame and glory - take up fishing! but don’t fall in - you may drown!!