The term “extremism” is indiscriminately bandied about today, applied usually to “conservatives” or to anything related to the “alt-right,” but rarely to the Left or to the straight-jacketed Trump Derangement inmates of the  MSM.

But, what does it in fact mean?
Wikipedia defines extremism as:
Extremism means, literally, “the quality or state of being extreme” or the “advocacy of extreme measures or views”.
Nowadays, the term is mostly used in a political or religious sense, to refer to an ideology that is considered (by the speaker or by some implied shared social consensus) to be far outside the (acceptable) mainstream attitudes of society.
Extremists are usually contrasted with centrists or moderates. For example, in contemporary discussions in Western countries of Islam or of Islamic political movements, the distinction between extremist (implying “bad”) and moderate (implying “good”) Muslims is typically stressed.[
Political agendas perceived as extremist often include those from the far-left politics or far-right politics as well as radicalism, reactionism, fundamentalism and fanaticism.
Extremism means, literally, “the quality or state of being extreme” or the “advocacy of extreme measures or views.”
Nowadays, the term is mostly used in a political or religious sense, to refer to an ideology that is considered (by the speaker or by some implied shared social consensus) to be far outside the (acceptable) mainstream attitudes of society,[2] but extremism can, for example, also be meant in an economic sense. However, all terrorists are extremists but all extremists are not terrorists. This is because extremism is only a belief or view that is seen as far-fetched by the public. Terrorism is the use of violence/intimidation in the pursuit of mainly political aims.
The term “extremism” is usually meant to be pejorative; that is, to express (strong) disapproval. However, it may also be used in a more academic, purely descriptive, non-condemning sense.
The Oxford English Dictionary defines extremism as:
The holding of extreme political or religious views; fanaticism.
The Compact Oxford goes into more detail:
Tendency to be extreme; disposition to go to extremes.
While extreme ,in the Compact Oxford, has half a page of definitions and usages going back several centuries, it begins  with:
Outermost. Farthest from the center; situated either of the ends.
The upmost point or verge;  an end , extremity.
The upmost imaginable of anything;…
Extremism could be taken as the statement “2 + 2 = 4,” written in secret by Winston Smith in Orwell’s Nineteen Eighty-Four, in Chapter IV.  “Freedom is the freedom to say that two plus two make four. If that is granted, all else follows.”  
Which is true. “All else”  includes especially mathematics. Two plus two make four leads to differential calculus and other subfields of mathematics.
He uses the phrase to wonder if the State might declare “two plus two equals five” as a fact; he ponders whether, if everybody believes it, that makes it true. Of course, “everybody” believing in the asserted truth of a statement comprises a consensus, a vote of hands to decide what is reality and what is not (true or untrue), not a reflection or expression of a truth.: “Fifty million Frenchmen can be as wrong as right,” as Ayn Rand once quipped. The phrase (“Fifty Million”) by Cole Porter, was popularized by Sophie Tucker in the 1927 musical of the same name.
Accepting a statement as true is not a matter of consensus, either. It is an issue of an individual’s recognition of a thing’s identity, based on the clear, unadulterated evidence of his senses together with the non-contradictory workings of his mind.  For example, a bowl of house keys will not create an edible bowl of Wheaties, no matter how much milk and sugar is added. It’s still a pile of keys. The identity of the keys, as inedible, non-consumable objects, is essential. It requires an uncorrupted mind to make the unqualified identification.  Keys must be recognized as keys, not as chunks of green moon cheese or flakes of wheat.
Virtually all of the definitions of extremism I encountered, while researching this column, employed, specifically or by implication, spatial measures. The term, however, as it is currently used by especially the MSM and the SPLC, to map out the political divisions in the country, is used exclusively to establish or identify the political references of individuals or groups, employing spatial measurements to identify purveyors of “hate speech,” whether or not they are separated by distance, or by the conceptual, normative differences in their ideas. Using only the idea of “hate speech” as a guide to organizations that actually or do not spew “hate speech” results in some correct identifications, but notoriously ridiculous groupings of non-hate speech groups with those notorious for it.
As I remark at the end of “Ignorance is Strength,” “Hate speech, when it applies to individuals or organizations to which the designation justly, actually applies, such as the KKK, the Nation of Islam, or The Daily Stormer, is just a lot of hot air.” Thus normative measures – valid or not – are used to identify individuals and groups the SPLC and the MSM choose to label as “hate groups,” allying the normative with the spatial measure, is invalid.
The SPLC defines a “hate group” as:
A hate group is a social group that advocates and practices hatred, hostility, or violence towards members of a race, ethnicity, nation, religion, gender, gender identity, sexual orientation or any other designated sector of society.
Thus, actual purveyors of hate speech are grouped with critical, journalistic individuals and organizations such as Jihad Watch, Pamela Geller, and The Investigative Project  on Terrorism. Thus, a virulently anti-Semitic  group such as The Nation of Islam is equated with any individual or organization noted for the critical examination of, or reportage, of the actions of Islam. The measure is moral; so that the grouping of legitimate critics of Islam, who do not advocate violence or force, with actual “hate groups,” who advocate violence or force, Extremism is about as invalid and nonsensical as passing judgment on the distance between Earth and Pluto.
Extremism, in today’s culture, is something to frown on regardless of whether or not it’s Left or Right, but especially if it’s Right. If the extremism is Right, if it advocates capitalism, then it is to be frowned upon, because it omits socialism or any kind of “planned” economic system in its  recommended social systems. Capitalism is also regularly equated with fascism, by both the Left and Right, even though historically fascism begins and ends with socialism, because fascism calls for a regimented economy, with nominal ownership of property. The SPLC and its yeah-sayers in academia, the MSM, and Hollywood propagate the fallacy insistently with no opposition or with the least evidence of thought.
“Hate speech” is likened to a bullet wound on some individual’s or group’s “self-esteem.” It must be banned or suppressed, the mainstream critics claim, lest it ricochet and harm people. In reality, hate speech has no metaphysical properties, as a bullet or knife does. Someone’s “hurt feelings’ should be that person’s business, with no legal recourse.
 Extremism is empty of meaning, as well,  even if the person or organization labeled as “extremist” is obnoxious (such as the KKK). One will be repelled by the literature or utterings of such an organization without  having to be told or mentally prompted. What must be realized is that both the terms “hate speech” and “extremism” are labels invented to protect one or another protected class:  Muslims, gays, LGBTs, immigrants, and all the other designated “victims.” Extremism is just another emotion charged term with which to smear that which is feared – facts and reality.