I´ve met 3 girls here who have all been in San Christobal for the same reason. There are 2 non-profits here that place foreigners in a Zapatista community for a week or two, simply to observe. I thought that the observations were to learn about their way of life etc. But it´s really to act as a "guard". The idea is that if the government comes into the community and does anything, then there is an outside witness from the international community. Kind of powerful stuff.