If people like playing Facebook games and you make money from it and enjoy making them, why not?
Have you played FarmVille at all? It's not your regular fun anymore, I assure you. It's completely built for addiction. I don't think there is any moral ground to justify this. Especially in a world where there is so little to keep our societies from sliding back into barbarism!
Oh come on. Don't blame the addict, blame the dealer? No one is forcing anyone to play Farmville. And btw, Zynga's stocks are tumbling and their player numbers are falling by the millions. I told you people would get bored with it.