I had to write an essay like this too. This is what I put:
France would profit:
Would become a country for the french again-wouldn't be formally attached to Europe anymore, more independence, don't have to pass certain regulations through someone else, just through their government
Bring back some french traditions which might've been lost. Lots of new holidays (ie Halloween) have been introduced into France since EU, aren't really a typical french thing, remind french people of what french values are. Would also mean that the french language would stay pretty much french, instead of English influences etc. They can still use English words without EU, but for some reason they seem to think that without the EU they would keep the frenchness in their language
Increase patriotism (dunno how, but it got me lots of marks!)
Own currency back, stabilises economy, enhances national pride (again, dunno how it makes you feel national pride but apparently it does)
They wouldn't benefit:
They wouldn't have ERASMUS and the other educational thing which I've forgotten, which help with international relations since the wars. Exchange programmes build bridges between countries such as France and Germany, which were the most affected by the wars. Also educates children of the cultures of others
Wouldn't have the secturity thing-more terrorism because they wouldn't be part of Europol *(previously interpol) which is an european crime buster system, controls borders, drugs trafficking etc means more illegal trade, immigration etc
Also not protected by EU in face of war. well they are coz the EU would help, but in theory they don't have to ( I think?!)
The EU is going to be the biggest trade power in the world, do they want to miss out on that?!
Tourism and leisure holiday makers could diminish because it would be difficult to cross the border into France (dunno, but would they still be part of the Schenge agreement if they left?)
Would Isolate themselves from European countries-negative affects for trade?????
Ok I'm getting stuck now, but those are the sort of things I would've wrote about!