I don't think anybody can map out any significant number of would-be- or already-editors who quit "just because there were no visual tool".
I have stopped editing because of harassment and wiki-stalking from http://en.wikipedia.org/wiki/User:WhiteWriter and no one stops him from doing the same to many other people. There are gangs of radicals that live on wikipedia and just make life miserable for others, and no visual editor will stop that.
mike
-- James Michael DuPont Member of Free Libre Open Source Software Kosova http://flossk.org