How to ditch WhatsApp.
A systematic approach in steps.
A thread.

Step 1: Install and Setup Alternatives

Here are some: Signal, Telegram.
If you're tech-savvy, also consider Threema.

For the rest of the thread, I'll assume Signal.

Also, install the web or desktop client.

Step 2: Enable Your Habit-Change

Add Signal to your home screen.
Remove WhatsApp from your home screen.
Make Signal your default.
Put Signal in the same spot WhatsApp had.
Whenever you want to message someone, check Signal first.

Step 3: Change your WhatsApp About

For example, to this:

For the sake of your and my privacy: Please use Signal instead of WhatsApp.

Step 4: Regular WhatsApp Status

Regularly set something like this as your WhatsApp Status:

Thanks to everyone that already moved to Signal.
Those who haven't yet, please use Signal instead of WhatsApp.

Step 5: Encourage Your Contacts

When you receive a WhatsApp message, tell the other party that you value your and their privacy, and because of that would prefer to continue the conversation on Signal if that's possible for them.

Step 6: Help Others

Help those family members and friends that don't know how to switch from WhatsApp to Signal. Explain to them why this is necessary (Facebook steals and sells your data). Install Signal for them. Then send them some funny stuff on Signal. Create comfort.

Step 7: Create awareness in Groups

If nobody has done it yet, briefly tell your group that you value your and the group members' privacy, and thus you are pondering about alternatives like Signal. Ask for volunteers that would install and try Signal.

Step 8: Prepare Moving Your Groups

Hold back some content that can be delayed for the moved group so the moved group will start with interesting content.
Find out your group's critical mass for moving.
Seek allies and consent for a move.
Then schedule and announce the move.

Step 9: Move Your Groups

For the actual move, remind group members. Get support from allies or co-admins. Create the new group on Signal. Add the group members.

Once complete or almost complete, DELETE THE OLD WHATSAPP GROUP!

Step 10: DELETE THE OLD WHATSAPP GROUP

Did I mention this? DELETE THE OLD WHATSAPP GROUP!

You don't want the WhatsApp Group to continue like a bad smoking habit.

Step 11: Start the Moved Group with Interesting Content

Take the content that you've held back (Step 8) and post it. This helps the new group in all kinds of ways.

Step 12: Support Other Groups Moving

Create awareness.
Collect data: Check how many group members are already on Signal.
Offer support.

Step 13: Create Awareness beyond WhatsApp

Talk about this on other social media, like Twitter, Facebook (yes, yes, I know, the irony), LinkedIn, Instagram, etc

Step 14: Check Success

Occasionally check-in on your own habits and the habits of your peers to make sure we're all moving away from WhatsApp.

Step 15: Delete WhatsApp

Delete your WhatsApp Account.
Remove the WhatsApp app from your phone.

This will take time.
I haven't reached there yet.

But together, we can do it!