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Against Silos+Signal
(www.moparisthebest.com)
XMPP (aka Jabber) is the community-owned standard for real-time federated messaging.
JoinJabber.org admin support chat
If this is your bar to clear, then WhatsApp should be fine.
Isn't whatsapp owned by Zucc?
It has end-to-end encryption and is used by billions of people. It's certainly a step up compared to FB Messenger.
The point is: if you are supporting Signal because of its usability and you don't care about giving up control to a siloed platform, then WhatsApp is already enough.