Oh, ok, I get the connection now, thanks.

My main point was not that I care about non-existing things in any way that conflicts with cares about existing things. My point was that believing in the concept of existence is not necessary for having preferences. I suppose I would agree with

A: Hmm, I guess I want [happiness of non-existing agents] too. However, that is negligible compared to my preferences about things that really do exist.

If not for the fact that I don't think existence has any meaning.