It has been a long journey.
I have been gradually convincing my family, close relatives and friends to make the switch to Signal for over two years. I am already the “tech support guy” in all my circles so most didn’t really question it. Most of my friends are quite tech-savvy, and some even did use Signal before I talked to them about it.
This also filtered out some “friends” who were never that close to me to begin with. So, that’s a bonus, I guess.
Overall, my recommendation to others interested would be to tell people how much you don’t like Meta’s business model instead of the privacy aspect. I already ditched Facebook and Instagram many years ago, and this helped defend my point a bit better.
WhatsApp has significant market dominance in Europe, to the point that only one or two people I know who live on that continent don’t use it. If you give someone your phone number in Europe, they will almost certainly send you a WhatsApp message, not an SMS.
It’s not a need in the sense that you’ll die without it, but not having it adds significant friction to social relationships.