The other thing to say about this is: I don't think helping strangers, or explaining to others how to help strangers - without any thought to what it might signal - is at all irrational.

I understand perfectly well, that for people with certain kinds of utilitarian goal systems, this kind of thing all makes perfect sense - and is absolutely the rational thing to do.

It is pretty strange that any such utilitarian people exist in the first place - but if we accept that axiomatically, things like the discussion on this thread follow - without any need for invoking irrationality.