"I must say that I have never experienced any bad behaviour from Bob"
I have
"there was a fight between them at a meeting"
Ewan was chairman at a discussion on folksong - Bob shouted down speaker after speaker from the floor, Ewan did his job as chairman and tried to stop him - Bert tried to calm things down - all recorded and archived.
Bob's diminutive size doesn't enhance his belligerence in any way and I've never seen Ewan strike a blow in anger throughout the twenty odd years I knew him - didn't come to blows but it wans't Bob's fault that it didn't.
"more deep seated than that."
Then you have to say what it was and not rely on rumours and urban myths.
A number of people may not have liked Ewan - he was dedicated to folksong and expected a degree of dedication from others who were involved because he believed folk song was important - a lot of people don't like that.
He could be cuttingly honest when asked his opinion - a lot of people are not too happy with that.
Some people didn't like Ewan's politics - I've been in clubs where he and members of the Critics group were asked not to sing political or even contemporary songs - it's happened to me several times.
I never found Ewan boorish or openly rude to people in public - he could become passionate in his arguments, but never in public.
You claim Ewan was boorish - when - how, certainly not at The Singers Club, or any other club where I ever saw him perform?
I always found Ewan far more sinned against than a sinner, as evidenced by that fact that, over half a century after his death people still regularly dig him up to give him a kicking.
Some time ago on this forum somebody told what, I presume, they regarded as an anti-MacColl story (as with the John Brune one)
If you saw him you will know that he had a habit of performing with his chair back-to-front (a marvelous relaxation trick, if you've ever tried it)
Apparently, when he came to one club, someone stuck a note across the back of the chair, unbeknownst to Ewan, saying "I am a twat" - hilarious and very professional!!   
I found Ewan easier and more rewarding to argue with than most people - including some of the members of the Critics Group - I had several heated discussions with him, on politics and on song, but we remained friends.
Ewan had far more to offer than just the songs he wrote and sang and it's having to plouter through stuff like this that prevents us from doing so - seems to me to say more about the destructive nature of some of the revival than it does about Ewan.
"a bit too much like National Service"
You had no alternative with National Service Nick, you could take the discipline of the Critics Group or leave it.
Ewan and Peggy, on a weekly basis, turned over their home to less experienced singers in order to assist them to become better performers - this went on for nearly ten years.
They put their book and tape collection at our disposal and quite often their spare (actually, young Calum's) bedroom so people could copy their field recordings and pore their way through their library.
In return, they expected a degree of commitment - if the group of us spent an hour working on somebody's singing, we weren't happy if they went away and forgot about it and did nothing, we expected people to put in work in return for our efforts
We committed ourselves to group work voluntarily because we believed we got something from it - if we felt we weren't, we didn't have to turn up.
It was the only way such a self-help study group could possibly continue to exist.
We did a similar thing with Singers Workshop, but we weren't as disciplined and we didn't achieve as much.
Jim Carroll