I think you are misunderstanbing. Mango "flowers" as a whole or the spike is a pannicle or inflorescence. Its not that spraying the pannicle or entire inflorescence that is bad, its spraying when the small individual flowers on the inflorescence are at a stage of open flowers that should be avoided. What harm could it cause? It can reduce or prevent the flowers from setting fruit if sprayed when the flowers or florets are at their open stage. What i am recommending is spraying the pannicle before the florets open, halting the process while the florets are at their open stage which is when pollination occurs, and then spraying again after you see the small fruit set (at the little green "bb" stage). The amount and frequency of spraying can be determined by you local weather or specific variety that may have a predisposition to getting anthracnose.
You dont have to listen or follow these recommendations however we are giving advice from experience. There are some growers who never spray copper ad have tremendous production, it depends on location.