Why should France stay in EU?

It is going to be a severe problem if you leave

First, it is difficult to leave the EU. A country that joins the European Union cannot just go at its will. Only recently, Britain invoked Article 50. This is the official notification by Britain of its intention to leave the EU. This is just one of many steps to leaving the EU.
Talks are raging that Britain will face severe levies, in the billions, for leaving the EU. Some EU countries claim that leaving the EU should be more complex and costly, ultimately stopping others from doing so. For any country considering leaving the EU, this is a significant deterrent.

The EU Nuclear Program

The European Union plans to develop its nuclear weapons program to counter Russia’s deterrent. The European Union will oversee the French nuclear weapons arsenal and will be under joint European command.
This will act as a deterrent to Russia and protect countries within the European Union. France could be subject to severe sanctions if it leaves the European Union. The European Union might also take a significant portion of France’s nuclear weapons arsenal for its use. France could face increased sanctions if it leaves the EU due to its nuclear capabilities.

Economic Impact

The EU offers its members many benefits, particularly in trade with other EU countries. All EU countries must follow a set of guidelines when trading with other European Union countries. Trade is the country’s most critical issue, despite the Russian and other deterrents.
France must renegotiate all trade agreements with the EU’s major trading partners if it decides to leave. This could lead to higher tariffs and increased costs and cause some countries to raise their trading prices with France.
This could create severe problems for the country, resulting in at the end of long-standing trade agreements. The campaign to leave the EU is primarily driven by the EU’s immigration policy and increased attacks on France.