To put it yet another way, Germany is not ready - and may never be ready - to provide implicitinsurance and underwriting for loans and investments made by Spanish banks, or Italian banks or French banks.
But if investors and creditors regard the proposals as credible, if banks are no longer considered too big to fail, the costs for banks of raising money would rise: as you will have deduced, the risks of investing in and lending to banks increases in proportion to the perceived reduction in the implicitinsurance against failure they receive from the state.