It seems that your argument then is that no one should ever be able to resell or give away anything that they buy ever. So when you buy something, anything at all, you would have to own it yourself until you throw it away. Obviously that would have a huge negative impact on the environment with items like cars, computers, clothes, etc. Also, the lack of a second-hand market would have a negative impact on low-income people who need to buy used goods for the lower prices. So it seems to me that your argument against the existence of any second-hand market would have disastrous effects and cannot exist in the real world.
You have avoided the issue of whether or not second-hand markets positively impact the primary market. For example, if people weren't able to sell their used cars, would they be more or less likely to buy new cars. I think that the answer is pretty obvious. If people couldn't resell their used cars ever, they would buy new cars less often. Mainly because people often partially pay for new cars by trading in or selling their old cars.
I agree with namlem's comment "Why does incurring the costs associated with resale on the industry in any way morally gray? It's the manufacture's right to price items accordingly. They can just raise it to compensate." The manufacture should simply price the existence of a resale market into their product. That's what ever merchant other than Steam already does.
Steam is breaking the law in the EU and their illegal business model (not allowing resales) is what allows them to undercut the prices of their competitors. Don't you find that to be a moral grey zone?
The problem with making the argument, as I suspect you are, that because games are intellectual property that they shouldn't be able to be resold when you are done with them, is that almost everything is intellectual property. Think of how many parts of your car are patented. Those patents are intellectual property. If you let Steam say that you don't own the games that you buy then you opening the floodgates to a world where you don't own anything that you buy - you are just "licensing" it. As I've stated above a world like that isn't practical and I don't believe it is morally correct either. It restricts the rights of consumers for no reason other than to further enrich the producers of goods, who many doing just fine as is. Valve is worth 2.5 Billion dollars. Aren't they doing well enough without having to step all over consumer's rights?