In 1983-84 the course, originally created by Jean Vuillemin, was taught primarily by Claude Puech (programming in Pascal, and basic algorithms and data structures), along with other instructors in analysis of algorithms (Jean Marc Steyaert), logic (Guy Cousineau), formal languages (Jean Berstel, Jean-Michel Autebert), and Petri nets (I have forgotten the instructor's name: Guy Vidal-Naquet, maybe?). I enjoyed programming, algorithms, and formal languages, and was particularly excited by algorithms. During the same year, in Math I took courses at Paris VII university, a mix of easy courses that bored me to death, and of more advanced courses that seemed to me too abstract and meaningless (Differential geometry come to mind - a course I only barely managed to pass). At the end of the year, I decided to switch to computer science and signed up for a DEA (Masters') in computer science at Orsay.
In retrospect, it is clear that Cours de Sevres was designed to lure would-be mathematicians into computer science by focusing exclusively on theoretical topics (I never understood why graph theory was not one of the topics taught), and provided an obviously biased image of computer science. Nevertheless it has had a lot of impact in forming many people who are now computer scientists in France.
So, I would say that deciding to study theoretical computer science was not a reasoned choice on my part, but largely a coincidence due to context. I never stopped to think about a profession as a way to contribute to society. I never considered how to best fit my talents and tastes to the potential needs of society in the coming decades. I simply picked a field in the same way that one picks a hobby: do what you enjoy, and if you succeed, continue. It is only a few years later, when I heard that I was recruited to CNRS and realized that I now had a job for life, that suddenly the question occurred to me: "What's the point?"
There is an inconsistency in this: I am against mandatory courses. Students only learn what they are interested in. You cannot take an ass who is not thirsty and force it to drink. Yet I would not have taken Cours de Sevres if it had not been mandatory, so my own experience goes against my own opinion!