If you add in the ability to downmod submissions this place will rapidly turn into Digg. i.e. An environment where a handful of people control the majority of the information.
As far as excluding TC content goes, while I could live without it, think about the number of AWESOME discussions that would have killed in the past, then ask yourself if that's what you want for the future.
A handful of people already control the majority of the information on this forum.
ValleyWag posted a flurry of articles which were counter to YCombinator interests and now ValleyWag articles are automatically posted with the dead attribute. The same scenario could happen with TechCrunch.
