OTOH, one intolerant/militant person can force an entire group to accept their opinion, if the people would rather accept their opinion than abandon contact/fri

OTOH, one intolerant/militant person can force an entire group to accept their opinion, if the people would rather accept their opinion than abandon contact/friendships with that person. If you force people to choose between using Signal and no longer being able to talk to you, they will make a choice. That choice could end with you being abandoned or ignored, or with a large group that would rather prefer WhatsApp using Signal, at least for this group. Especially if it's multiple militant people, this effect can be quite powerful.