Church taxes are not at all uncommon throughout Europe, though Germany has the most extreme example. This applies not only to Catholics but to all Germans, regardless of confession. It is the primary means that churches in Germany have of raising revenue.
I personally don’t agree with the idea (I think each individual should have to voluntarily support the Church through donations outside of tax), but it is what it is.
The problem is that by renouncing their membership in the Church to the State officials, the people referred to here have formally renounced the Faith. Technically, that makes them apostates (or at a minimum schismatics).
Can. 751Heresy is the obstinate denial or obstinate doubt after the reception of baptism of some truth which is to be believed by divine and Catholic faith; apostasy is the total repudiation of the Christian faith; schism is the refusal of submission to the Supreme Pontiff or of communion with the members of the Church subject to him.
And what is the penalty for apostasy or schism?
Can. 1364 §1. Without prejudice to the prescript of can. 194, §1, n. 2, an apostate from the faith, a heretic, or a schismatic incurs a latae sententiae excommunication; in addition, a cleric can be punished with the penalties mentioned in can. 1336, §1, nn. 1, 2, and 3.
The actual decree from the bishops state:
Die aus der Kirche ausgetretene Person
- darf die Sakramente der Buße, Eucharistie, Firmung und Krankensalbung – außer in Todesgefahr - nicht empfangen,
außer in Todesgefahr means outside the danger of death. Again, strictly in accordance with Canon Law.
For somebody who might call this simony:
Can. 222 §1. The Christian faithful are obliged to assist with the needs of the Church so that the Church has what is necessary for divine worship, for the works of the apostolate and of charity, and for the decent support of ministers.
Think about it in this country: to have a child baptized, you need to be an active member of the parish in which the child is to be baptized. To have a child confirmed, the same thing. To get married in the Church, the same thing.
Don’t get me wrong, I never have liked the idea of a Kirchensteuer, but if the German people don’t like the idea of this, they should work to change their laws…not renounce their faith in order to avoid the requirements of their laws.