The Associated Press style guide weighs in:
“Alt-right” (quotation marks, hyphen and lower case) may be used in quotes or modified as in the “self-described” or “so-called alt-right” in stories discussing what the movement says about itself.
Avoid using the term generically and without definition, however, because it is not well known and the term may exist primarily as a public-relations device to make its supporters’ actual beliefs less clear and more acceptable to a broader audience. In the past we have called such beliefs racist, neo-Nazi or white supremacist.
AP explains the reason why:
Finally, when writing on extreme groups, be precise and provide evidence to support the characterization.
We should not limit ourselves to letting such groups define themselves, and instead should report their actions, associations, history and positions to reveal their actual beliefs and philosophy, as well as how others see them.
Exactly. And while we are on this, there is no such thing as the “alt-left”, either. As far as I can see, the “alt-left” is something the right-wing media cobbled together in a spirit of ‘your momma’ name-calling, turning a label they dislike back on their political opponents.
George Orwell in a timeless essay warned against such imprecision in speech and writing:
Each of these passages has faults of its own, but, quite apart from avoidable ugliness, two qualities are common to all of them. The first is staleness of imagery; the other is lack of precision. The writer either has a meaning and cannot express it, or he inadvertently says something else, or he is almost indifferent as to whether his words mean anything or not. This mixture of vagueness and sheer incompetence is the most marked characteristic of modern English prose, and especially of any kind of political writing. As soon as certain topics are raised, the concrete melts into the abstract and no one seems able to think of turns of speech that are not hackneyed: prose consists less and less of words chosen for the sake of their meaning, and more and more of phrases tacked together like the sections of a prefabricated hen-house.
In passing, replugging here an earlier post on the “left media” red herring (Since I wrote this post, by the way, “left media” has lost most of its meaning through overuse, forcing Arnab Goswami to come up with a new one: “Lutyens media”.)