Here's a spin on your question: let's say you asked somebody in the West (say, a street performer) if you can take their photo, and they asked you for money. You would consider if the amount being asked is reasonable, and then either take the photo and give them the money, or you would not. However, you would presumably not start arguing with them about whether "it's the right thing" for them to ask for money, or for you to give it.
This applies equally anybody you meet in a remote 3rd-world village. Many photogenic tribes (long-neck Karens, Maasai herdsmen, Aboriginal dancers in Australia, etc) are quite well aware of the fact that Westerners consider them photogenic, and not a few make a living off this. So, if they're asking you for money, and the amount they want is reasonable, pay them.
That said, it's tough to separate this from the subjective "should you" discussion: for example, many Karens in Thailand are there as refugees with extremely limited job options outside posing in human zoos for tourists, and the lucrative industry built around this both encourages the status quo and drives young Karens to join it. But if you're concerned about exploitation, the correct response is to not go on organized tours in the first place, so the middlemen don't get their cut.