The privilege of free speech doesn't mean that you can say what you like, when you like. Society functions because there are checks and balances, and unless they are observed we're faced with a chaotic situation. What some people call 'good manners' is simply a way of acknowledging the sensibilities of others, and affording them a measure of respect.
If parents can't be bothered to teach their children how they should behave, the state may decide to do it for them, via legislation. When that happens there's a danger that legislators, influenced by various interested parties, will over-compensate, with the inevitable media-exciting results.