1. The baseline is not the money made selling, but the capital _gain_, that is income, not revenue.
2. Keeping those 15% social charges into account negates the fact that those will accrue your retirement, invalidity, unemployment, what-have-you fund
3. France has a 35 hour workweek. Companies who ask their employees to work longer than that without compensating them in extra days of holiday are breaking the law. So much for the quoted 70 hour workweek.
4. The 10 years of uncertainty are not so uncertain in a country with such a strong welfare state: in case of failure you would have several months of unemployment checks which have a very high cap (as demonstrated by a recent scandal with soccer players).