While yes there needs to be an end point to the conversation I don't see some negotiating as bad. Learning how to express what you want and to justify it is a life skill all people need to develop.
One more thing that might help is to avoid language like "you were bad." It really isn't very specific and it does open you up to the question about being good. So, it might eliminate a bit of the trouble if you use very specific, related consequences. "Because you broke the computer rules, no computer for one week." Kid: "I want to use the computer" Parent: "I know you do because you really enjoy the computer, but you broke the computer rule so no computer for one week. What do you think you'll do first when you get your computer privileges back."
