This topic has come up before many times and the fact is these people who are eating the pigs need to learn proper agriculture and 'green' environmental practices. In this day and age, every resource must be conserved and efficient practices are paramount in keeping the earth a viable place to live for future generations.
Eating guinea pigs is hardly the cure for hunger or a 'way out' of being poor + hungry. Livestock can perform many useful functions, in rural china people use water buffalo for hard labor, dogs for gaurding livestock, etc. If you have pigs as pets, you know how much one little pig eats and poops daily. Likewise pigs are hardly labor animals and cannot pull farm equipment, gaurd livestock, provide milk, or such. One is infinately better off growing vegetables and grain or rice for own self and family, eating them rather than feeding them to a pig long enough for the pig to become an adult, then eating the pig. If one is going to have animals, at least have animals that provide a useful purpose like milk or labor. Many cultures have existed this way since ancient times, look at the predominance of agriculture in ancient China, Japan, etc.
All too often cultures use non-green or non-sustainable environmental practices, and it has lasting impact on the environment even today. For instance the ancient arabians with their nomanic practices and large herds of defoliating animals (primarily goats) led to the formation of the sahara and other middle eastern deserts, wastelands that still exist even to this day. A more recent example is the destruction of much of the west (buffalo, land, etc.) as america expanded into the west. With expanding populations, if the earth is to be habitable for future generations, we do not have the convinience of allowing non-environmentally conscious practices to go on simply b'cos they are part of this or that culture. It would be no different than if I said overconsuming, waste, and pollution is part of American culture, ever since the industrial revolution, and hence no one has the right to say we cannot waste, pollute, and degrade the environment to our heart's content.