"he said everybody should sing songs indigenous to them"'
He didn't - he said people should sing songs in their own accents, Lomax and Lloyd argued the same.
The reason was to persuade people to direct their attention to opening up their own local and national repertoires instead of sounding 'oirish' or mid-Atlantic - it worked.
The argument was first put forward by Lomax at a time when Lloyd and MacColl were doing both - they succumbed to his reasoning many people stopped sounding like "Walthamstow cowboys galloping across the plains of Essex" - to quote Peggy, though sadly, many others didn't.
Peggy's letter on the subject is still on the 'Living Tradition' archive, but I'm happy to dig it out if anybody doubts it.
Jim Carroll