The long and the short of it is that Germany and France are independent, soverign nations. The confederacy was not.
The strongest argument against any Frenchman or German arguing that their respective nations are independent and sovereign is the existence of the EU with its common currency and fungible citizenship. For every Frenchman or German willing to argue the point, there are two who will gladly take the other side.
The argument of any Frenchman or German against the effective consolidation of their nations will be: (1) their cultural distinctiveness and (2) the fact that their armies are not yet consolidated (although this is in the planning stages). Those arguments redound in favor of the Confederacy's sovereignty - not against it.