Funny thing is that it mainly seems to be the music sessions that object to singing, not vice versa.

And for the very good reasons already given........

However, it also seems that tunes sessions are the only ones that are forced to be placed in the position of having to object.

As I say - few tune session particpants do object. But that does not make the practice of insisting on flouting the convention - the correct or the polite thing to do.

When you attend a song session - you accept that you will be part of an audience - rather than a participant - for most of the evening - waiting for your turn to lead a song (except for joining in the chorus).

When you attend a song session - you expect that you will not be part of an audience at all - but a participant for most of the evening.