More accurately, black lives don't matter any more or less than white lives, Asian lives, Hispanic lives, Native Indian lives or any other lives. They all matter. And to that end, everyone should be treated equally under the law. That is a conservative position, not a liberal one. Liberals build so much of their belief structure on special treatment. As if two wrongs will ever make a right.
Special treatment sews the seeds of division and animosity. It doesn't help people understand each other. I'm not suggesting that your cause is completely pointless, rather that your approach is flawed.
If you are a "black lives matter" protester, or supporter, think about that with respect to how to achieve your goal of having people realize that equal treatment under the law is your objective. Of course black lives matter - the only ones who don't realize that are homicidal maniacs and hard core racists. But you will get much more buy in from everybody else if you changed your slogan to something more all-inclusive, like:
Every life matters.
I'm just suggesting that you'll get more buy-in that way, rather than being confrontational. Think about it.