Isn't it a function of what kind of gathering it is?

If it's supposed to be a primarily instrumental session, then instrumental tunes should be expected to be the norm, with songs only now and then, at most, and you wouldn't expect a non-playing singer to attend unless he/she/it liked to listen.

If it's a performers' circle, with people taking their turns in order, then it ought to be each person's option - unless it was announced as a "song circle," which at least implies vocal, rather than instrumental, stuff.

The problem arises with a spontaneous jam, where no rules have been set in advance. If there's a consensus as to what kind of music you're there to do, fine. If not, you may have to break up into two or more sessions.

I sing, and play mostly backup guitar, except alone in my kitchen late at night, where I'm free to play a tune, get halfway through, lose it, swear, and start over. (The cats don't mind.) So I'm glad to play backup for instrumentals - for a while. Then I get bored and leave. But I don't "resent" instrumental tunes being played unless the session was announced in advance as primarily a singing one.

There's a great quote from Chris Newman in the new Flatpicking Guitar magazine, that I posted here once in another thread, but I think is relevant to this one:

Q (Dan Miller): Since there are not too many lead guitar players in Irish
and Scottish music, do you find that other musicians will typically want you
to stay in a rhythm role when you get together to jam:

A (Chris): Absolutely. It is one of the reasons I don't play sessions in
pubs and things like that. Sessions in pubs on guitar playing Irish and
Scottish music is the most boring job in the world. I've got no objection
at all to playing rhythm all night. I actually enjoy doing that. But
playing rhythm to eight fiddle players who are all trying to play louder
than you, I can't be bothered. I hate all that and avoid it like the
plague. But in a good situation with a couple of other musicians,
especially if you are the only guitar or chord player there is great fun.

Peter.