[jansan]

There has been masks around for more than 100 years to protect from infectious diseases. Why is this still an ongoing debate?

[Nursie]

The ongoing debate is whether getting the general public to wear masks is actually helpful or not.

See my other response for ways in which that differs from medical staff doing it. It's psychology and sociology as well as pure "can a mask stop the virus", which are important factors when looking at disease transmission in a population.