Second, the Vatican has fully supported them on this. Quite rightly so. Perhaps you are unaware, but the way you exempt yourself from church tax in Germany is by publicly renouncing your church membership. You either go to a magistrate or to the parish office in person and formally renounce your allegiance to the church of your baptism. Someone who publicly proclaims that they are no longer a Catholic has excommunicated himself and forfeited the sacraments. In fact, the gall of someone demanding the sacraments after openly committing apostasy is morally repugnant.
Third, many Germans who pay no church tax - because they are poor and do not have sufficient taxable income - are still very welcome. The issue is not one of payment, but of public renunciation of the Church.