Jazz is a kind of music that relies greatly on emotions. It’s highly improvisational, and improvisation picks up the mood of the moment and goes with it. The stronger the mood, the livelier the improvisation.

In the 1920s, jazz’s ability to work with emotions was one of the reasons why it was so strongly opposed by the more traditional section of society. Jazz music, with its fast, syncopated rhythm, was thought to be able to bring out the more basic, primitive, animalistic emotions. And the dances that were danced to it (the Charleston, the Black Bottom, the Turkey Trot and such like) didn’t do anything to mitigate that idea.
People would dance in couples to that music, often embracing each other, their bodies rubbing against each other, at a fast, exhilarating rhythm. That was the good of jazz for young people, it was the freedom to express themselves, a liberating experience, both physical and intellectual. Jazz represented the brake away from the past. It was a new rhythm, a new way to understand rules, even a new way to bend those rules to create something that didn’t existed before.

Most traditional people thought this was true… only it wasn’t good at all. The break away from the past and conventional rules were perceive as something that would eventually destroy society. The ‘devil music’ would twist young people’s inhibitions and moral restraints – especially those of women – and would create rebellion against authority, which would eventually lead to chaos.
And if this were not enough, jazz was performed in disreputable places (mostly speakeasies) where other illegal activities were going on (drinking and interracial meeting), which the music seemed to encourage.
It was clearly the making of the devil and some reformers asked that it be prohibited just like alcohol.

But on the other side of the fence, jazz is understood in a very different way. As Wynton Marsalis explains in his book Moving on Higher Ground: how jazz can change your life, the most important emotion jazz encourages is respect.
Because improvisation is so essential to the life of jazz music, it requires a very strong feeling for the group. Musicians have to be aware of what they have to offer, but they also need to be aware that all the other musicians and even the listeners have something just as valuable to bring in. That’s how you recognise everyone’s potentiality and how you create something by making it work together.
At its heart, jazz is a great song of freedom and respect.

Marsalis, Wynton, Moving to Higher Ground: how jazz can change your life. Random House, New York, 2008

Jazz in America – What is Jazz?
Medical Daily – Emotion and Creativity: Jazz Improvisation of Happiness Activates Different Brain Networks than Sadness