I am making no generalisations whatever and I ma not talking about ancient songs
Our actual knowledge of what we know of the oral tradition is confined to what was collected by Sharp and heis colleges, and a little earlier from Baring Gould and even then, little was collected by way of information and    opinions of the singers (Roud points that out)
We have little else other than an examination of the contents of the songs - my points on the social contents are confined to the 19th century, when the songs that were collected then were possibly made.
Some features of the songs date back many centuries and remain unchanged, particularly the social misalliance and arranged marriage songs.
"On what basis do you characterise the writers of broadsides as outsiders?"
The folk songs we are dealing with are largely rural (a constant description of them ahs been "Country Songs", and those of small communities based around mining and textiles, alongside sea and military songs.   
Unless you are suggesting (as Steve Gardham has), that the hacks worked on the land or served at sea, etc., they were desk-bound, Urban based outsiders.
It is infinitely more sensible to think that the folk songs that reached the broadside presses were brought back in skeletal form by packmen, or gathered from visiting countrymen, or soldiers embarking for foreign service, or sailors in port.
Seven Dials was within pissing distance of Covent Garden, where farmers wiould come to sell their produce and Smithfield where country livestock would be brought for sale - the docks were well within walking distance
Yet we are told that it was the desk-jockeys who created the realistic pictures that the songs presented
Sure they did!!!
It really boils down to this
If you accept that 'ordinary' people were capable of making songs there is no reason on earth to suggest that they didn't create our folk songs
You need to remember that we are viewing the dying embers of a tradition, and a miniscule part of it at that, limited to where the collectors worked,
This is why I suggest we need to look elsewhere in these islands for other explanations
We worked in with Irish singers - the rural population lost their tradition in the 1950s, so our singers were a part of a living one - the Travellers had a creative oral tradition up to the point where they acquired portable televisions in the mid 1970s
We spent a great deal of time recording our singers talking about how songs worked within their communities
One of our most important findings was of the large repertoire of songs that had been made locally during the lifetimes of the singers - on every subject under the sun - on local railways, maritime disasters, emigration, evictions, land protests, national ist warfare, murders, drunken nights out... all operating side by side with centuries old ballads and songs and obviously having been used to make new songs
The Scots had a similar situation going for them, particularly in the bothies
Either the English people did the same ot they were far less creative and imaginative than their neighbors
You decide
Jim Carroll