Red herrings are responses to arguments that ignore the argument and focus on something else. Many, but not all, have Latin names beginning with argumentum ad. Not all argumentum ad fallacies are red herrings, of course.
Nor are they all formal fallacies. Some, such as the argumentum ad Hitlerian, the claim that what you say is false because Hitler once did or said something similar, are more in the line of cute observations rather than official fallacies. For the record, it’s merely a subset of ad hominem with a little “poisoning the well” thrown in for good measure.
Argumentum ad consequentiam
In 1975, the Birmingham (UK) Six were sentenced to life imprisonment for the Birmingham pub bombings, an attack attributed to the Provisional IRA that killed 21 people. The six men claimed to have been brutalized in police custody. Fourteen prison officers were subsequently charged with assault, but were acquitted. The Birmingham Six continued to appeal, but their case was thrown out by Lord Denning of the Court of Appeal, who wrote these amazing words.
“If [the six men] won, it would mean that the police were guilty of perjury; that they were guilty of violence and threats; that the confessions were involuntary and improperly admitted in evidence; and that the convictions were erroneous. That would mean that the Home Secretary would have either to recommend that they be pardoned or to remit the case to the Court of Appeal. That was such an appalling vista that every sensible person would say, ‘It cannot be right that these actions should go any further.’”This is an example of argumentum ad consequentiam, the “argument to the consequences.” The truth of the premise is determined by whether it leads to desirable or undesirable consequences. The legendary attempt by a Tennessee legislator to pass a bill making π = 3.0 was based on the premise that it would make math so much easier for high school students, who wouldn’t have to wrestle with all those decimal places.
This is not to say that consequences don’t matter, or that they shouldn’t affect decision-making. It’s only that consequences, no matter what they are, don’t determine the truth of an argument.