I'm late to the party. First of all, I'm a deaf person. I've been on both sides of this issue. JWs found me through their 'canvassing' and when I was a JW, I saw they had a list of deaf people in whatever territory.
Yes, I am aware it is similar in other languages but let me tell you this. The deaf community is not very big and pretty much everyone knows each other. Interpreters knows our private lives due to interpreting for us.
When I found out the JWs had a list of all deaf people, I asked how did they obtain the name, address, etc? They said it was through canvassing but I soon found out that some brothers and sisters obtained the information in an unethical way and broke confidentiality rules.
I take offense in how they obtained the information! I work right inside the deaf community and I'd be crucified if I ever witnessed to my clients! I refused to witness to them because I felt it was wrong for me as I was someone that they trusted to keep their information private. When I took the job at work, I was bound to ethical and confidentiality rules.