Is there any evidence of this? Do you have any research showing the correlation of the rise in Facebook to increased mob violence in the world. The world has actually enjoyed a few decades of low violence compared to the historic mean.
"The Mission has examined documents, publications, statements, Facebook posts and audio-visual materials that have contributed to shaping public opinion on the Rohingya and Muslims more generally. The analysis demonstrates that a carefully crafted hate campaign has developed a negative perception of Muslims among the broad population in Myanmar. This campaign has been the work of a few key players: nationalistic political parties and politicians, leading monks, academics, prominent individuals and members of the Government. This hate campaign, which continues to the present day, portrays the Rohingya and other Muslims as an existential threat to Myanmar and to Buddhism"
I'm not even sure I can take the second point in good faith. Violence having decreased compared to historical high points has literally nothing to say on whether social media itself causes violence. Other factors can easily explain an overall decline, which obviously is not uniform. If you live in one of the countries in which social media is used as a means to instigate genocides, I can tell you that more safety in a US city will matter very little to you.
[1]https://www.nytimes.com/2018/11/06/technology/myanmar-facebo...
[2]https://www.ohchr.org/Documents/HRBodies/HRCouncil/FFM-Myanm...
Furthermore did the lack of Facebook produce better outcomes for Muslims in China? The world is complicated place, the answer probably isn't as simple as "Facebook is bad".
And again, the issue is not the state of violence in the world or just Facebook, which is why I used 'social media' more generally at the end of my last post, it's the ways in which those companies uniquely contribute to violence.
You don't need to be responsible for all violence in the world to be held accountable for the violence you cause. The fact that the world is complicated and violent doesn't absolve actors from their responsibility. Social media is quite unique in many ways. From mass bot-networks to influence campaigns that disguise themselves as bottom-up, to speed and virality that no other medium has, to lack of accountability and the ease at which information moves cross borders and enables nefarious states to conduct sabotage.
And China is not a good example either. It's probably the prime example of a country that has used digital technologies, including social media, to build a dystopian surveillance network, including on Uyghurs, that could not otherwise function.
Also the question to your answer is likely both, as in there's a feedback loop between real world violence, causing more conflict on social media, fuelling yet more violence.