Good argument, but it can work against you just as easily as it can work for you. If you don't show shipping charges at the cart level, many people may be forced to register to see the charge, and then perhaps they leave after they see the price. One way to help with this is to provide a shipping calculator before checkout or at the product level if you don't have it already.
I, for one, refuse to buy from a site that sends me an e-mail asking me to complete my purchase. If I wanted to complete the purchase, I would have done it while I was there
