Is It Right That Germany Gets to Tax Bitcoins?

Legal tender is a medium of payment issued by a government that must be accepted by merchants for the extinguishment of debts within the government's respective country. In other words, the government guarantees that I can exchange the paper in my wallet for goods and services in my country. I pay taxes for this promise to be facilitated. No ice cream vendor can deny me an ice cream cone if I have the correct amount of legal tender to pay for the cone.

This brings me to my next point: how does the German government have the right to tax bitcoins if they are not forcing all merchants in Germany to accept bitcoins as a form of payment? Germany forces merchants to accept euros for payment of goods and services -- this keeps the system working for everyone. However, if I had all of my money in bitcoins (for whatever reason), and the German government is taxing me on my transactions, shouldn't my medium of exchange be given legal tender rights? Or am I looking at this the wrong way?