Immediately reminded me of the Blue Whale challenge, a VK-based hoax that led to alleged suicides, arrests, and moral panic across Russia.
And what happens when an incitement to violence can be shared instantly with hundreds of people who can each share it with hundreds more?
Compare also RTLM, a Rwandan radio station that played a central role in the propagation of genocidal calls to action. I'd argue that whatever communication technology prevails can (and sadly probably will) be abused to incite violence. This is not a WhatsApp-specific problem.