is in many ways a matter of materialism v idealism.
Another point:
While I personally am quick to throw around the "materialism" vs "idealism" contrast, I think we need to be clear what it means. Epicurus doesn't hold that things need to be "material" in order to be felt -- he says mental feelings are stronger than physical ones. So "idealism" can certainly cause pleasure and pain, I would presume, and that makes idealism at least as "real" as dreams in that idealism can affect us.
This gets blurry as well in asking "are we talking about concepts vs things that have a material existence?
I think we need to be clear in what respect saying that something is "idealism" means something. "Capitalism" and "communism" may not exist as independent entities, but they do exist as "concepts" or "ideals," and a lot of tears have been shed over "capitalism" and "communism" just the same, so they are certainly "real" in that they can cause pain or pleasure.