In order to decide whether it is right for you to ban certain topics, you need to consider the current subject matter of your community. It would be unwise to ban controversial topics that are intrinsically part of your community. For example, you will find it unworkable to prevent discussion of politics within a current affairs forum. You need to consider what effect banning certain subjects will have on your online community and whether such bans would even be workable.
General interest communities will find it far easier to make certain topics off-limits. Indeed, the topics you are thinking about banning may rarely get a mention in the first place. In this case, it is far easier to make certain topics off limits as there are still plenty of other subjects people are able to talk about. The benefit of general interest online communities is the fact that they are not dependant on discussions on a specific subject.
Perhaps the most controversial topics within an online community are religion and politics. These subjects can raise the emotions of those discussing them, which in turn can create friction and arguments of an extremely personal nature. On the other hand, such topics can really draw people in and create a huge amount of interest and interaction within your community. If you decide to pursue this strategy though, you will need to ensure you can provide thorough and timely moderation.
Another factor you should consider before deciding whether you should ban certain topics from being discussed within your online community is what types of members your community attracts. Mature, rational members will tend to cause fewer problems than a membership base of younger, more sensitive members. All online communities are different - what works for one community may not work for yours. Only make decisions based on what works for you and your members.
I always recommend light forum moderation - after all, you do not want your members to hesitate when it comes to posting and creating content. Banning members and editing posts will not create a positive atmosphere. You should always start off by giving your members the benefit of the doubt. Let them discuss anything within reason, and only act if certain topics are repeatedly causing you problems.
Remember; the more restrictive your online community is, the more you are discouraging interaction. This is not the path to take if you wish to develop a thriving, vibrant community.