Strictly speaking, even if your used purchase isn't directly adding to the demand for new products, you are indirectly feeding that demand by supporting the used market. A strengthened used market better enables those who sell their used computers to generate capital to buy new. So while you have a valid case for saying you're not adding
as much to the demand, don't think you're not adding some to it through your used/refurb purchase.
(you are of course free to disagree, I'm not here to convince you and am not going to argue the point)