I think that as a whole, we often don't respect cultural differences. Comments like "Silly Americans..." and worse on this question are common. Having a location tag won't prevent people from making such comments. If it did result in greater respect for cultural differences, I would go for it in a heartbeat, but I don't think that's the case.
Another reason (besides ineffectiveness) is that users might not answer, thinking, "Oh, I'm not Asian, so I can't answer that for them."
I'm not Asian, but I can answer parenting questions to the best of my ability. We all face difficulties and we all have valuable experiences to share. I've learned things from people in the UK or Scandinavia that I would not have been exposed to here. I'm glad they shared their perspective freely. I am not in favor of anything that might hamper an answer.
We're all human, we face similar difficulties with raising our children or setting boundaries with our parents. Knowing the culture might encourage users from the same culture to answer within that framework, but I think more than that, what we need is respect for differences.
If someone posts about spanking their children in a culture that encourages spanking, we don't need a lot of answers (not just comments, but answers) about how stupid and barbaric that parent is. We need respect enough to point out the consequences of spanking (teaching abusive practices, etc.) and propose better alternatives.
If someone posts about a privacy-invading parent from a culture that tolerates parental authority until death, and we withhold a reasonable, respectful answer that would make the OP's life easier, that would be sad.
I don't think a location tag will solve these problems.