Don`t worry about that . It`s a common mistake among language learners .Keep talking , no matter how many errors you make . You can improve it by reading as many story books as you can ..Try to listen a lot too. It will be excluded gradually.

The passive form was used because someone else banned using it . That`s why we use these sentences. ** Smoking is banned in some public buildings. (e.i : it is banned by the government) **Smoking and mobile phones are banned on flights. (e.i : like the above one) I think hunting should be banned. (i.e : should be banned by the authority )