I rise to the defense of non-existing things (for a non-existing retainer, so I guess this is pro bono).
Hypothetical, possible, and future things are important things to talk about. How impoverished we would be if our minds were limited to what is actual. There would be no art, no growth in technology, no progress in culture without imagining what it is like to live in a better world. Novelists and actors feel themselves haunted by their characters - they aren't mad, they know what is real, but non-real things can have realistic qualities. We have to make a distinction between things with the attribute of existence and things without it to talk about this strange, wonderful, useful, essential part of our humanity.