Black lives do indeed matter, at least to the extent that any lives do.
We refer to black lives separately instead of interjecting the stupid ALL lives matter because we're specifically addressing the murder of African Americans by racist cops.
Coming back with "all lives matter" is a cheap way of getting off the serious subject.
All life appears to be a net-negative experience right now. because right now, the rewards don't come close to adequately compensating the travails--even in the most privileged lives.
As for Antifa,
Anti-Fascist=good.
Fascist =bad.
What's the problem?
Comparing just political movements to orangutan rallies, which truly are KKK rallies in every practical way, is simply stupid.