Germany in its constitutional law has protections against that data being used for any other purpose or government agencies. Does that help if a new antisemitic party would take over? Not likely for long, but hopefully long enough for other constitutional protections (like banning the party), anti-fascists or people working there themselves to intervene. On the other hand folks like the CCC or other data protection NGOs have been trying to teach politicians data minimalism for a while, but in this particular case religious conservatives don't want the state to get out of collecting church tax and the churches don't want the state to get out of it. In particular, Jewish communities could request the state not to collect taxes, tell their members to not enter that data into the tax forms and collected tithes/donations/similar on their own.

IBM designed and serviced such a system when it was known to be used by a genocidal government as the customer