A lot of unspoken assumptions are linked to where someone's from or where they live, and having an idea about these unspoken assumptions can in turn help preventing or mitigating crossed wires.

Those "unspoken assumptions" are nothing but assumptions on your part. Which really has nothing to do with disproving what someone actually says. Your saying that through the internet, with a complete lack of communication ques other then written words, you can reasonably draw these "unspoken assumptions" based on someones nationality? And that you'll argue those assumptions to the other person, even though their "unspoken"?

No, it helps YOU draw assumptions about what they know or do not know. Which has nothing to do with disproving something with facts. How could it possibly help you refute something someone says to know what country they are from? The only way that would work is if you accept the "Your from... So your wrong. Period." school of thought.

Knowing where someone is from would help me decide whether I need to explain more, what to explain, how I can use comparisons to explain my case, etc. The biggest source of discussion is the fact that people often miscommunicate. Even when they agree, it can take while until they figure out they agree. Knowing the other guy's background can help tremendously. Discussion is not only about the differences between opinion. It's also about how to reach agreement.