Will alone bin log ignore DB mysql helps in slave read only mode Please correct me if I'm wrong . 
In Master - Slave setup:

Case 1:


  If I didn't  enable Binlog ignore DB mysql: In future ill lose all
  users created in master node incase of master crash or slave to master
  and master to slave scenario.


Case 2:


  If I did enable binlog ignore DB mysql and an user has  all
  privileges, he can directly connect to slave DB[if he is fishy], and
  manipulate data in slave which causes inconsistency.




How to over come this scenario? I'm new to this. Any help is highly appreciated.
After series of testing.. this scenario only happens if we grant all privileges on every database (.)[ I think it will assume this specific user as root privileged and allows to access any database. In any other scenario it will reject with below error.

*ERROR 1290 (HY000): The MySQL server is running with the --read-only option so it cannot execute this statement*