Pro :
- Only one level of corruption instead of two to keep in check.
- A (sometime too zealous) protection of the language.
Against :
- Less international political weight
- Companies forced to to business in french by law might gtfo since it incur costs
- Weak military power (would we stay in NATO?)
Globally :
Our roads are already crap. Healthcare is free but your experience in quality of service might vary. We already selling our natural resources like there is no tomorrow and we store nuclear waste here too.