Part of the problem is that the majority of 'Folkies' are FAR too polite , and will 'put up' with ALL sorts of incompetent singers and musicians , rather than risk offending somneone . I am something of a 'noodler' myself , but all it needs is a 'look' and I will stop ,
though a lot of people who know me suggest a key or start note to me !
The Sensitinity thing works both ways though - IF joining a session , DONT just leap in , and if a stranger joins your session , try and help them find their feet !