An interesting argument, but one with which I don't agree. To give up on something because someone else says its undoable is certainly un-brilliant; but I can understand being demotivated by someone's argument that your goal is worthless.

Recall that the guy is in South America, where many millions of people still live in the most grinding poverty; I can understand why a teacher would argue that since videogames are toys for rich kids, it's self-indulgent to devote oneself to such a thing when only a day's journey from the university (or maybe less) there are people with no clean water, access to medicine, etc. Now, I actually think a South American videogame compny would be a fine thing in the bigger context: it would create jobs, diversify the economy, could lead to new educational tools and so on. Videogames certainly stimulated my interest in computers and technology and still do. But while he may be brilliant enough to become a fine game programmer/designer/businessman, I can't blame him for being socially and economically immature enough that he's not able to see how it all fits together.

so my answer would be 'you love video games? Then make some, the world needs better games, because games can be powerful learning tools'.