Type: Informal Fallacy
He who knows only his own side of the case, knows little of that. His reasons may be good, and no one may have been able to refute them. But if he is equally unable to refute the reasons on the opposite side; if he does not so much as know what they are, he has no ground for preferring either opinion.
Source: John Stuart Mill, On Liberty
You've spoke about having seen the children's prisons in Iraq. Can you describe what you saw there?
Source: Massimo Calabresi, "Scott Ritter in His Own Words", Time, 9/14/2002
A one-sided case presents only evidence favoring its conclusion, and ignores or downplays the evidence against it. In inductive reasoning, it is important to consider all of the available evidence before coming to a conclusion. For example, suppose that you have observed several white swans; then you might conclude:
All swans are white.
However, if you have observed even one black swan, you should not come to this conclusion. Instead, you might draw one of the weaker conclusions:
So, the total evidence available to you consists in observations of several white swans and a black one. Whatever conclusion that you draw needs to be consistent with this evidence, but "all swans are white" is inconsistent with there being even one black swan. To leave the black swan out of your reasoning would be One-sidedness.
It is by no means always fallacious to present a one-sided argument. As is usual with fallacies, we have to take the context of the argument into consideration. For instance, a trial attorney presents a one-sided case in favor of a client. It is not a defense attorney's job to present the evidence for the defendant's guilt, rather that is the job of the prosecutor. Likewise, the prosecutor's job is to present a one-sided case for conviction. Both sides are presented in a trial, just not by the same persons. This is the way that adversarial systems, such as the legal system, work: each side presents a biased case, and the jury comes to a decision based upon hearing both sides. In this way, even though each side is slanted, all of the relevant evidence is presented by whichever side it happens to favor.
Other contexts of argumentation are similarly adversarial, for example, partisan politics such as election campaigns. A candidate's campaign will present only a positive case for the candidate's election, and a case against the candidate's opponents. However, the other side can always be relied upon to present the negative case. We voters, by listening to both sides of the campaign, can make an objective decision about how to vote based upon all the available evidence. This is why it is important to pay attention to all sides during a campaign, and to hear different political points of view. People who listen to only one side will inevitably form one-sided opinions.
Another major source of non-fallacious bias is in the world of advertising. We have no reason to expect advertisers or salespeople to tell us what is wrong with their product, or why we should buy some other manufacturer's product instead. This is why we should take such pitches with a heavy dose of skepticism. Unfortunately, all too seldom do we hear the other side of the argument, as promoters of products seem to be reluctant to criticize competitors. As rational consumers, we need to turn to consumer publications to hear the other side of the story.
One-sidedness is fallacious in contexts where we have a right to demand objectivity. Two such contexts are news stories and scientific or other scholarly writing:
It seems to me there are many kinds of one-sidedness that are strategies more than arguments. For example, what I call "controlling the microphone." If somehow one side can control when a microphone is turned on (literally or figuratively), then the opposition may not be heard. If one side controls access to mass media, to certain publications, etc., then only their side is presented or their opponents' arguments are filtered to their advantage. Congress has variants of this, for example, "filling up the amendment tree" which prevents opposing amendments from being added. Or simply limiting debate before all the issues have been aired. The judicial branch may deny someone a hearing which lets the status quo stand without further argument. Large advertisers try to fill the airwaves with their pitch, leaving little space for the opposition. I'm tempted to call these something like meta-fallacies or hyper-fallacies because they aren't arguments per se but strategies for promoting something.―Ralph Gillmann
I would resist the temptation if I were you. A "meta-fallacy" would be a fallacy about a fallacy, and a "hyper-fallacy" would be a fallacy on steroids, neither of which seems right. The examples that you give are all good examples of what I call "boobytraps", that is, nonarguments that can cause someone to fall into fallacious reasoning. Much of what is called "slanting", or―in the context of propaganda―"card stacking", is the setting up of one-sided boobytraps.
Slanting can be one of the most insidiously deceptive boobytraps, because simply leaving out relevant information can lead people seriously astray. In order to do this, dictatorships and totalitarian governments have always attempted to monopolize the news media and education, in order to control what information people receive. It's almost impossible to detect such one-sidedness if you lack other sources for the relevant facts, which is what makes a free press so important.