"Ewan wrote a lot of songs from other people's characters."
As far as I know MacColl took all the songs he wrote in the person from acutuality (one of his constant song-making practices) - Shoals of Hering from Larner and Ronnie Balls, Freeborn man from Minty Smith, Belle Stewart, Gordon Boswell etc., Just a Note and Drivers Song from Jack Hamilton, Shellback from Ben Bright. Can't recall him writing songs in first person on Apartheid victims or miners, though I know he occasionally used commentary from news interviews (I actually gathered some of these cuttings for Festival of Fools sketches).
I believe that what he did find 'dishonest' was some of the pastiches, where the writer pretends to be an 18th century highwayman, or a 19th century sailor under sail - he argued that many of them sounded arificial and many appeared to have come purely from the writer's imagination rather than reality.
To me, this sometimes to be the case, though I'm not sure it isn't a generalisation on his part - I have always been totally smitten with Rosselson's 'Digger's Song'.
"Lillibellero"
The song that sang a king out of three kingdoms (James II)
Jim Carroll