Probably repeating someone else's point already, but I will just say it again to repeat.
Do not enforce rules due to emotion. Promote free speech by engaging in potential discussions and not trolling them whenever they appear, do not be PC.
On top of that, being nice is unnecessary. It is just a drag for those whom you know need improvement but you have to be nice because you don't want to hurt their feelings. What you want to be is good. To be good means to constructively criticise with the intention of improving the persons skills or views and not to laugh or make fun of them.