HGiles: Used games are definitely legal. Once a person buys something, they own it.
As the poster above me already mentioned, this unfortunately isn't correct anymore. It depends on where you live.
Here in Germany, the Verbraucherzentrale (our version of a BBB) actually went to court to prevent media publishers from prohibiting customers to resell digital products. They went to Germany's highest court and unfortunately lost. The judges stated that the new business practice was legal as long as no physical product was shipped, and explicitly recommended people to not buy digital-only products if they don't agree with the "no resale / you don't own your purchase" business practice; he apparently expects the market to sort things out. It's unfortunate, one may not agree with it, but it's the law now.
HGiles: Psyringe's argument is false on a couple of levels. The exact places s/he is wrong differ depending on who you ask, but the basic problem is that s/he's treating buying something like charity, so there's a basic logic fail there. Also, s/he's claiming that every person who uses a product should pay the person who originally produced it.
I have no idea where you got this from, it certainly wasn't part of anything I said. What I'm saying is that 1. Gamersgate explicitly sells their games under the provision that they are non-transferable once downloaded, 2. that this is part of the contract one agrees to when buying games from GamersGate, and 3. that giving said games away to someone else violates said contract. This is objectively true and can be checked by anyone who can be bothered to look up the actual facts at the GamersGate site.
I also voiced my concern that violating this agreement hurts GamersGate's business, which in the long run will hurt the paying customers. This is an opinion, but one that's backed by basic economics and that has proven to be true often enough. In no way did I mention "charity" or made the other claims you read into my post.
This part of the discussion started as a question about the long-term availability and safety of products bought at GamersGate. It was not intended to be a discussion about the legality of resales or about economic systems and law. If I see people using this discussion (and the info provided) to propagate violating GamersGate's terms of service and spreading Gamersgate products to people who haven't paid for them, then it will do more harm than good, and I will feel compelled to remove my posts and ask the moderators to remove the others. So please stop. Feel free to write me a PM if you do have a desire to discuss the issue with me.