My opinion is that if gringo tourists didn't demand such foods (re: Jim Sloan at the top of this thread), then the corporations would be less inclined to proliferate worldwide. Yes, I know that the local folks love their McDonald's and Pollo Kentucky, but the spread of these super-chains leads me to believe that much of this is driven by gringo tourist and expatriate demand.
This malignancy isn't limited to fast food.
A good friend of mine who is also my financial guy recently took his family to Cancun. When they ran out of some essentials, he took his family not to the wonderful open-air markets, not even to the local shopping mall Cancun 2000; rather, he sought and found the nearest Wal*Mex.
Instead of exposing his young sons to local culture and customs, instead of immersing himself and his family into the culture, he took the easy way out, as so many of us do when traveling.
I'm not a real experienced traveler; I've been to Amsterdam, paris and Madrid in Europe, twice to Mexico and twice to C.R. I am proud however of the fact that i have only eaten in local restaurants and have only shopped in local markets. Screw the chain stores and fast-food giants. The taste of a mamon chino bought at 400 colones per kilo beats a McDeadCow every time.
Sadly, the cancer of American megacorporations cannot be stopped, and the Wal*Mart model will continue to take over the workplace. Soon, the ubiquitous megacorps will become both the new government and the new religion. God save us all.