<< Its my beliefe that if debt should be assumed commonly, it will break up the EU because no voters in any country would agree to this. >>

But that's exactly what happened in the early days of the founding of the US, when Alexander Hamilton negotiated the Funding Act of 1790: "The Funding Act authorized the federal government to receive certificates of state war-incurred debts and to issue federal securities in exchange." https://en.wikipedia.org/wiki/Funding_Act_of_1790

Without the Funding Act, the state governments would've defaulted on their Revolutionary War debt. By assuming the debt of the states, the US greatly strengthened their collective borrowing ability and also brought the states closer together into the union.