Lets assume that instead that money would go to the employee and not to social security. And we will assume that a large house would cost about 500k EUR. Thus, in 40 years, you would have collected a million euros more. That is about 25k EUR extra per year. That seems to be about the amount of income tax a French citizen would pay every year.

Thus, that money doesn't just go to health care. It also goes to other social security programs and government projects.