You might have some imperfect obligation to speak out against some issue. (It can’t be a perfect obligation, can it? Does anyone think you are literally obligated to speak out for or against some issue at all times you’re awake?)
Even if so, it doesn’t follow that other people have permission to make you speak out on demand. For instance, even if you should speak out against the genocide of the Uighurs or against closed borders (two things that are far more important, morally speaking, than Black Lives Matter), it doesn’t follow that I, Jason Brennan, may approach you at any time and insist that you speak out on the spot. If I further harassed, harangued, and threatened you, you would be justified in defying me.
At any rate, I am please to report that last night in DC, I found that exactly zero protesters were wearing “Free the Uighurs/F**k the CCP” or “Open Borders” T-shirts. I beat up 300 people with a baseball bat, thus protecting the world from their horrifically violent silence.