If a forum is not specifically about political current events, then you are usually not allowed to talk about political current events there.
Many forums not dedicated to politics have an official or unofficial ban on discussing current politics. (Historical politics, as long as it doesn't involve comparing others to Nazisnote , is usually okay if relevant to the matter at hand; 20 years seems to usually be the threshold for "current", with a few notable exceptions.)
The reasoning is quite simple: Any discussion of current politics is likely to lead to a Flame War. Unnecessary flame wars are bad. Thus, any discussion of politics is likely to be trolling, although you will get the occasional Naïve Newcomer who genuinely doesn't know any better. Thus, the Ban On Politics.
Politics is not the only subject that gets this treatment, but it is the most prominent; both sex and religion also get this treatment, but both are usually more prone to self censorship anyway. There is a long-standing belief that one should never discuss sex, politics or religion at dinner parties. Of course, in Real Life, dinner parties that do discuss these topics are always the fun ones. Regardless of that, the point is that some subjects can create fights, and thus many forums ban these subjects.
Around here, we call our version of this the Rule of Cautious Editing Judgment.
The only exception is, obviously, articles about politicians, which we try to treat with all the delicacy and care typically reserved for land mines. Keyword being "try", since we usually have chronic edit wars anyway, but hey, we need the articles for completeness' sake.
A worldwide Ban On Politics has been adopted by a large number of Freemason lodges (which frequently extends to a ban on religious talk as well, to discourage arguments between members of different sects or religions). Their dinner parties are said to be the most pleasant and friendly ones on the planet.
A slight variation on the Ban On Politics often exists in environments with some degree of internal politics, for similar reasons of stopping incipient fighting. For example, a forum may ban some or all discussions of moderation or administrative actions if these discussions have previously led to Flame War, a venue/bar might ban a band if its presence leads to a Bar Brawl, or a group of any sort may bar an individual whose presence fractures the unity of the group for some reason or another. Another similar variation is the "ban on discussion," e.g. closing a post of some sort to comments entirely if it is in regard to a sensitive issue and/or people cannot stop fighting in the comments/attacking the poster.
Ironically, the opposite of this trope is not too rare either. Meaning it is permissible to talk about current political events, but against the (written or unwritten) rules to talk about general political issues. This is likely because if you take a general political topic, like socialism vs. conservatism (or other types of ideologies), it will often be the same old forum members who come up with the same old arguments that they cannot account for and use them as an excuse to flame each other (or new members who interfere by doing the same or are ganged up on by older members). While with a current political issue, it is often easier to research it thoroughly and have some facts to back your arguments up and there is a fair chance that the discussion will stop once the issue stops being commonly brought up in the media, while the formerly mentioned discussion of socialism vs. conservatism will likely continue as long as humankind is alive. Similarly, debates about concrete issues can be based on concrete facts - general debates tend to be based much more on feelings and philosophical / ideological differences.
- In The Exception, when Wehrmacht soldier Captain Brandt is about to be introduced to the former Kaiser Wilhelm II, the Kaiser's adjutant Siguard lays out some ground rules, including the forbidding of political discussions.
—Colonel Sigurd von Ilsemann: You'll address him as sir and his wife as madam. The Treaty of Versailles forbids any other form of address. His left arm is slightly deformed; you will not refer to it or look at it. You will speak only when spoken to and all discussion of politics is forbidden. Express no opinion of your own, agree with his and remember, at the age of four, he bit the Duke of Edinburgh in the leg.