If it is clearly unsafe to speak out based on what's happened to others who have done so, it is not necessary to voluntarily stick your own head on the chopping block. That's the time to hoist the Jolly Roger and start cutting throats.
And hoisting the Jolly Roger* and cutting throats won't lead you to the chopping block? Violent revolutions may be proper at times, but they are certainly no way to avoid being "killed or disappeared." The point is that either route will be dangerous to your health, but which is appropriate to the situation? It seems to me that violent overthrow must, first, be morally justified; and second, enjoy popular support. Otherwise, you're just having a temper tantrum that gets you, and the cause, in worse trouble.
Jim, MLK's approach worked. He was killed, and it still worked. If I remember right, PRESIDENTS OF THE UNITED STATES, as in more than one, were listening to the man. His approach swayed public opinion. Black Power violence would only have proved that Blacks were a dangerous race to be kept in their place by repression and occasional lynchings.
*the Jolly Roger is a symbol of either freelance piracy, or piracy in service of a hostile govt. Either way, this is an odd symbol to use for the defense of one's rights. Yes, I know, it comes from a well-known quotation.