@sir82, I think your conclusions are premature. Yes, ECJ has decided that EU data protection law is applicable to door-to-door notekeeping and JW entities are responsible for compliance with that law.
But it should be noted that, for example, art. 6(1)(f) of GDPR allows processing of personal data, with the exception of data revealing racial or ethnic origin, political opinions, religious or philosophical beliefs, data concerning health, sex life or sexual orientation and other sensitive data, without consent of data subject when "processing is necessary for the purposes of the legitimate interests pursued by the controller or by a third party, except where such interests are overridden by the interests or fundamental rights and freedoms of the data subject". Taking into account that The Article 29 Working Party mentioned exercise of the right to freedom of expression or information, conventional direct marketing, other forms of marketing or advertisement, and unsolicited non-commercial messages, including for political campaigns or charitable fundraising, as possibly being legitimate purposes of data processing (Opinion 06/2014, p. 25), it will likely be necessary for national supervisory authorities and courts, CJEU and other national and international bodies to determine whether and to what extent that provision is applicable to JW door-to-door ministry and similar activities (e.g., political canvassing).
As Steve Peers (University of Essex) wrote,
But while we know that EU data protection law applies to such activities, and that responsibility is shared, we don’t know how to apply the law in such cases, as the Court wasn’t asked. (The earlier ruling on home security cameras similarly leaves such possible questions unanswered). On what grounds can the data be processed? Must homeowners give their consent to the processing for specific reasons? One can imagine that those who are already reluctant to discuss their faith with Jehovah’s Witnesses will be even more reluctant to discuss the minutiae of data protection consent with them too. Can the legitimate interest of evangelists or political canvassers justify the processing of data? Or can a statute validly regulate this issue? (One suspects that politicians will be particularly keen to find time to legislate to justify their own activities, if necessary).
Finally, I don't think that not-at-home and do-not-call data are personal data and protected by EU law.