I usually begin teaching this song with a noticeable chuckle from the group. To "sing Kumbaya" has come to imply useless gestures at unification and bridge building, a normalized snarkiness that seems to assume the inevitability of divisiveness between people.  Perhaps the song was overused in the sixties and seventies and thus became a stereotype.  But this song, in its time, as a part of the powerful civil rights movement and so many movements that have permanently changed the consciousness of this country, it shouldn't be overlooked.  
     The story often goes that Missionaries in Angola taught the words "come by here" to natives, and their accent/pronunciation stuck, with the song arriving back in the states as "Kumbaya".  But this story is most likely erroneous and seems to come from a single pastor who liked the story.  There are recordings from the twenties, and it surely comes from even earlier times, amongst Gulla peoples, and also from Tennessee. It's important to know that there are varying opinions of how this song should be sung.  I've heard an account of Ysaye Barnwell insisting that it is a lament, and shouldn't ever be sung as a light or joyous song. It was passed to me by a Pastor at Village Fire who I believe made this arrangement, and he encouraged its use as a community prayer.   Here is an article with more on this song.