Isn't the very existence of Signal "activism".
The thing is, for me to exercise my right to privacy, it helps if I can practice that right with more than one or two people in my address book.
And it didn't take much effort. The desire for a cross-platform (iOS/Android) group chat system, Signal's features like desktop apps and ease of use, and a generally growing dislike for Facebook/Meta made it pretty painless and organic.