Addictive games that are addictive because they're compelling products that people have fun with? I find it hard to have any ethical qualms about making those. I have been a victim of Civilization's "just one more turn" effect since the early nineties, but I don't think there's any ethical stain on Sid Meier, Bryan Reynolds, Soren Johnson, or any of their teams. Sure, parts of these games could be viewed as psychologically manipulative, but then again, so could changing elements of a website according to psychological principles to increase conversion. The ethics and morality of using these tools hinges on intent.