Given his position, Zuck's response is understandable, but at the same time I find it distasteful to refer to employees writing "All Lives Matter" as "malicious". What they are saying is valid and accurate. I do not see it as insulting at all, but rather a broadening of the statement to be fully encompassing and supporting of all people (isn't that what embracing diversity is really about?!).
It's hard to understand being lashed out against for arguing that all people matter equally.
For context, see this recent post:
"Zuckerberg Asks Employees to Stop Crossing Out “Black Lives Matter” at FB HQ (techcrunch.com)"
https://news.ycombinator.com/item?id=11176467