I can'y comment about kennedy's treatment of people he collected from, I don't know anything other the gossip you pick up. But I do have a serious criticism of his intellectual honesty, whicjh I think is important in the collecting business. For instance, in his big book(cant remeber the title,Folksongs of britain or somesuch) he printed the Cornish songs with the words translated into Cornish. Now, that would have been fine as interesting footnoes or something, but he put the Cornish words in just the same same place as the English words of other songs. This amounts to me as passing off a counterfeit as the real thing: in fact there were tiny footnotes which if read carefully would tell you that they were in fact translations, but you had to be really concentrating to spot them. I know for a fact that this deceived some credulous people into believing that these Cornish words were the originals of the songs. I believe he also rewrote a lot of songs and passed them off as something he had collected, though I have no definite personal knowledge of this. These two points I do find worrying: if someone claims to be a collector, you should be entitled to take what they offer you as what they collected, not something they've made up to back up some theory or other.
    But in general I'm with Captain Birdseye: he left us a fantastic treasure chest of music, and there's maybe not a great deal of point in being too picky about how he went about it, now he's dead and gone. Let's just relish what he rescued. But while relishing it, take it all with a pinch of salt!