Stardestroyer.net fits that description somewhat, for values of "casually" that allow for copious swearing punctuating most disagreements. I haven't posted there, but Kaj Sotala posts as Xuenay (<s>apologies</s> no apologies for stalking).

Examples of threads on LW-related topics:

• Logic Fallacy reference thread Mk. 2
• The Singularity in Sci-Fi (haven't read)
• Robots Learn How to Lie
• Mini-FAQ on Artificial Intelligence (the thread that properly introduced me to SIAI)
• This derailment about Three Worlds Collide
• Rationality (short)
• And the Winner for Most Probable God is... Azathoth?
• Transhumanism: is it viable?

(Edited after first upvote; later edited again to add a link.)