According to the good people at Funk & Wagnalls Standard Dictionary, the definition of the word rant is as follows: "a noun meaning to speak in loud, violent, or extravagant language; rave." Seeing as rave is part of the definition, in an effort to be thorough I checked it out as well: "To speak wildly or incoherently."
According to that definition that means when we talk of somebody ranting, we're implying they are frothing at the mouth like a rabid dog, and spewing out massive amounts of insensible verbiage. It would seem to me that our current usage of the word is slightly more tolerant than that formal definition. In fact, I feel confident in suggesting that most people would agree that a rant is an impassioned statement about any subject a speaker or writer has strong feelings about.
Rants aren't even dangerous - usually they're just a really good way for a person to let off steam about something that's ticked them off in the moment. Unfortunately, some people live up to the dictionary definition, frothing at the mouth with hatred and ending up leaving a sour taste in most people's mouths. It doesn't have anything to do with political affiliations; hatred knows no party lines and left or right can be equally to blame.
The best types of rants are those undertaken by intelligent people with great senses of humour. They are those people who won't be tied down by political affiliations or dogma, and have no problem with taking on idiocy no matter who the source is. The only people who need fear them are the self-righteous, the pompous, and folk who take themselves and their opinions far too seriously.
A few years back Canadians were introduced to the comic genius of Rick Mercer when the satirical news/current events show This Hour Has Twenty-Two Minutes started being televised on the Canadian Broadcasting Corporation (CBC). More recently they have welcomed him into their homes as host of the Rick Mercer Report. Now thanks to Random House Canada and their imprint Doubleday Canada, we will now know him as an author. September 25th sees the publication of Rick Mercer Report: The Book, a compendium of interviews and editorials (rants) from four years of the show, and selected articles from his blog.
Rick is originally from the youngest province in Canada, and the one primarily known around the world for it's "barbaric" seal hunt: Newfoundland. Being from Newfoundland is an important part of Rick's makeup as a comic. Newfoundland didn't become part of Canada until 1949 and has been the poorest province since. When the Cod fish stocks failed and the seal hunt became unpopular, villages that had been first settled in the 1700's began turning into ghost towns.