“We must not overlook the role that extremists play. They are the gadflies that keep society from being too complacent.”

I am sure that Osama would agree. But in the days when this was said, extremism was not so often so extreme; at least not in the West. Then came the Second World War, which, with the expansion of communications media, exacerbated the growth of violent tendencies engendered by the First, and now you know the rest of the story. I think that the word "extremists" now carries a violent connotation, which perhaps it did not for Flexner.

Yes, I agree, the choice of the word "extreme" probably meant progressive in those days.

I think what the other posters are missing is that there is a very marked difference between "extremist" and "violent extremist".

Our complacency is allowing our government to destroy us. Now they are reaching out to control the rest of the world through the United Nations. Is it any wonder extremists resist our socialist offers? They are less than complacent and are resisting our "help". If our government left the Middle East to its own control, most extremists (terrorists) would have little reason to bring their anger to our soil. BTW, if terrorists (foreign or domestic) come to your home to kill you, will you remain die complacent or fight back to live?

Gee, Joe, it all depends. I mean, are the terrorists who come to kill you socialist-liberals or ultra-right death squads?

'Extremist' is a word used subjectively, of course, as it is always in reference to something 'normal' or 'common'. So, in general, extremism does play an important role in challenging old beliefs and the structures that have become entrenched around them -- when the fallacy is known, the structure comes crumbling down -- thus the efforts to silence extremists by those with the most to lose.

The man who said this lived from 1866-1959. The word "extremists" had an entirely different context in those days...and not necessarily a scary one. In those days, and I was alive then, an extremist was a purist...one who made sure that what they did hung together consistently without contradictions... But, violent extremists came into play with the World Wars and others...so that now we know, that certain philosophies and outlooks, when purified, lead to violent extremism. Incidentially, Hitler was not a right wing extremist...his party was the National Socialist Party...so judge for yourself. History teachs alot when you can get a good version of it....or are willing to listen to those who have lived it and can see the repetitions.

Nicely put, Archer.

Under any understanding of extremists (old, new or what ever), the persistent irritating critic or nuisance disrupts, even for the slightest of moments, the serenity of the smug's complacency. A gadfly can be a provocative stimulus for the good or the bad. The occupying statist theocracy infesting this land has dummied down its helots, serfs, slaves and otherwise ignorant patrons sufficiently that complacency has been taken to a whole new level.

We are the keepers of sanity..... Margaret Mead was right on!

The medical professions, far sighted, see very clearly the effects of certain cultural habits and their inevitable effect on a wholesome society. That is not rocket science. Extreme ignorance plays well into the hands of the democratic socialist movement world wide. Without extreme measures of the educated extremist, this nation would never have been founded. Make no mistake, it was painful and violent ! The passive far left, is anything but passive ! Made evident this election season 2016. Enough is enough ! Reprobate mindsets should never be allowed to rule !

"Extremism in the defense of Liberty is no vice."