This is basically my entire point and I think you've explained better than I could originally.
Private sellers on eBay have decided to sell the item for one reason or another and chose to place the item for sale in an auction where shipping costs will be incurred. I don't think the buyer should be paying every last cent it costs you to ship the item (at the very least, costs shouldn't be added to profit from shipping on top of the selling price). And of course, the other side can always be argued.