Well, before WWI quite a few people considered the economic interdependence of the European states big enough to prevent big wars. They were wrong. Who says that we're right when we claim the same thing? Just look at Russia - there you can see without trouble that politics still trump economics.
Economic interdependence was not significant, English and German economic rivalry guaranteed military opposition and free trade was sought, instead protectionism and imperialism. Lacking any notion of mutually assured destruction, the British believed they could secure victory in one decisive naval victory as in Trafalgar, the French believed they could as in Austerlitz and the Germans as in the Franco-Prussian war. When the two armies mobilized for war they envisaged quick, gargantuan yet decisive battles ruled by mobility of cavalry and train - not the devastating trench warfare to unfold.
Nowadays with free trade, no Empires to support protectionism and immense economic interdependence the European states cannot wage war upon one another, (Germany and Britain for example could not even start a trade war let alone a military one and hope to have any gain), and with mutually assured destruction there can further be only civil war.
Just look at Russia. Not only was Germany, France and the UK incapable of delivering devastating sanctions needed to cripple Russia, they limited it to arms embargo and freezing of the Russian cabinet's assets held in the West. And look at who provoked this war - the Germans and French warned George Bush that giving NATO membership to Ukraine would be an unnecessary provocation and force a military confrontation, as the Russians cannot tolerate Western soldiers within quick striking distance of Volgograd.
2007 - EU and Ukraine begin talks of integrating the country offering closer economic and political cooperation. Free trade negotiations begin in tandem.
2008 - The Russio-Georgian war begins and prompts a quick condemnation from George Bush, seeking to expand NATO membership to Georgia and Ukraine, whilst removing Russian opposition to missile defence systems in Eastern Europe. Angela Merkel is upset and angry. Germany and France say they believe that since neither Ukraine nor Georgia is stable enough to enter the program now, a membership plan would be an unnecessary offense to Russia which firmly opposes the move. Putin, has threats to cancel his planned visit to the NATO meeting on Friday if the two former Soviet states enter the program for eventual membership. Senior German diplomat, Wolfgang Ischinger, says that offering membership to a divided Ukraine could destabilize the new government there, and that not enough diplomacy had taken place beforehand with Russia.
The EU Commission that year begins talks in Brussels of visa free travel between the EU and Ukraine.
2009 - the EU-Ukraine Association Agenda is adopted. Its intentions included promoting a gradual convergence toward the EU's Common Security and Defence Policy and European Defence Agency policies. Eastern Ukraine is lukewarm, Western Ukraine supportive.
2010 - the French constitution is modified in order to remove compulsory referendums for the accession of Ukraine and Turkey to the EU.
2012 - the EU-Ukraine Association Agreement is initiated in Brussels but not signed, with EU leaders citing their opposition as resulting from Ukraine's deteriorating democracy.
2013 - President Barroso makes it clear to Yanukovych that Ukraine cannot both be a member of the Customs Union of Belarus, Russian and Kazakhstan, and a member of the European Union. The Russians and the EU attempt to compromise with individual treaties, observer status of the Customs Union without membership of it and statements of neutral intent from both sides.
2014 - Prime Minister Azarov's admin draw up the plan to be implemented upon Ukraine and the EU's ratification of the Association Agreement. Yanukovych's refusal to sign the Association Agreement leads to protests, his security forces' crackdown and escalation leads to the Euromaidan revolution. The Russians denounce this as a coup and Eastern Ukrainians begin stirring up trouble. The Crimean peninsula is annexed by Russia. Russian humanitarian convoys begin entering Eastern Ukraine, carrying paramilitary soldiers and equipment to launch a covert invasion.
2015 - the Minsk II ceasefire is placed in effect with no significant territorial changes, turning the war into an unresolved conflict.
The other big danger is: What if France elects an irrational leader who does not see those benefits? Or, God forbid, my countrymen do? Especially in an economic downturn, where those benefits are less pronounced, this is a real possibility. And in such a situation the old saying 'Blood is thicker than water' holds true: Friendship can wither, so it's better to be brothers than just friends.
You would have to elect an irrational leader who is incapable of seeing there is nothing to be gained and much to be lost completely unrestrained by the workings of the state, nothing I expect to see from anything short of a military coup. And then what? It would take the dissolution of NATO and rapid rearmament escaping the attention of the USA by one of Europe's two nuclear powers. Neither Britain nor France hold the capability to occupy Europe in the event that they conquered it and their home nations were fine with their actions.
You are also yet to demonstrate why in response to the threat of imagined warlords you would rather preemptively surrender all of your sovereignty just to avoid fighting against a threat that does not exist! Switzerland is your neighbour, if Germany or France were genuinely worried about having to fight off foreign invasion why didn't they keep NATO membership or adopt armed neutrality instead of surrendering everything?
This line of thinking, it is sadly too influential. It is one the biggest talking points by the remain campaign and none of it makes sense. You don't defend against enemies by giving them your country just to spare them the effort of fighting your soldiers, and these enemies are yet to appear! Why do you give away everything just to avoid losing it to enemies that do not exist?!!
And where ideals and political views are concerned, the (EU) European nations are pretty similar already, so living under the same roof would hardly be a burden. It would be different with, let's say, Russia - that's why I'm not advocating the integration of that country, at least not to the same degree. But where's the fundamental gap between a German dude and a Frenchman?
Besides one being German and the other French, it is as you say their differences shall become irrelevant and not even Russians or Turks will escape integration.
Well, it's equally important to me that it's possible to kick my country in the teeth as well - I thought that was a given. Again: I find the idea of one country dominating its neighbors to be abhorrent.
Then why do you support the EU? Its inception, purpose and practice is hegemony