I would argue it’s even better role play if players don’t know things though. If you meet some followers of Bane, a player who knows the lore will probably deem them to be a bad guy. If they have no idea, they will roll knowledge to see if their character would know. The DM providing information based on character knowledge checks is generally a great source of fun.

The DM saying “yeah I know you know Bane is a bad guy but I made your roll for it and you failed so you need to pretend you don’t know that” is never very good even if the players try to obey the spirit of things.