In most cases, the established social norm will already have been set by the time you arrive, and you may not even be given a choice in your decision. In heavily touristy regions in poor countries that have been exposed to Western tourism, most people will demand money for photos, and whatever you choose to do (cooperate or not) will not have any effect on that society. Most tourists go to Rome and do as the Romans, and there's no way to reach enough people to affect change.
So, paying for photos in this social climate is not objectionable, per se, although it is quite sad. Hence, I don't have a problem with this, but I must say, from a purely photographic standpoint, such situations rarely yield good photos anyway. Sure, upon first seeing people in a striking environment, you are tempted to snap away, but after you see beneath the surface and get to know people, you may find these initial "paid-for" photos to be inferior to those where you've engaged and become familiar with a chosen few. (And if you do that, chances are, they won't ask for money anyway.)
