As Moxie Marlinspike once said, the fine line between facism and social democracy is choice. In order to exist in certain social groups, you have to expand your scope of choice to be able participate. In my experience using TextSecure/Signal for a decade and having convinced all of my friends/immediate family/significant others to use it, the majority of new people that I have encountered even with Signal installed on their phones, do not use it. It’s unfortunate, but most people only care about privacy to a certain degree, if at all. What I usually do is bite the bullet with SMS for a bit. If things are going somewhere, I eventually convince them onto Signal. If things don’t pan out, then not too much damage done.

Could not have said this better.

The Signal protocol (née TextSecure protocol) was created by Moxie Marlinspike and Trevor Perrin and Signal messenger (née TextSecure) was built from the ground up with e2ee. WhatsApp was acquired by Facebook without e2ee and Moxie later worked with them to integrate the Signal protocol for WhatsApp. Hope that clarifies.