Nobody I know wants United States of Europe. The European Union is completely undemocratic at it's core, our national leaders have made sure that the electorate has minimal powers and influence over their supranational policing. Sovereignty of the people conflicts with the sovereignty of nations.
I do want the United States of Europe. The alternative is the return of walls, nationalisms and wars, which has been the natural state of affairs in Europe for 99.9% of its history (100 years ago the Ministry of Defense was called Ministry of War for a reason). The iteration we have at the moment is far from efficient, far from perfect, far from fair, but it's better than anything that has come before.
No it's not. You can have an EU-lite, where we agree on some things, like free trade, joint projects (like EuroPol). Not having the United States of Europe won't result in war any more than the EU imposing a rule on an non-volunteer country will.
If anything the EU has shown that it doesn't work. We can't even agree on helping people fleeing a war zone. Nor are the Eurozone countries in agreement on how to handle financial policies.
It's not that the European countries should work together, or strive to have similar laws and rules, but it should be limited to issues like trade and the environment. Things that is beyond the scope of single nations.