Yes they are morally indefensible. Many of those decisions didn't make sense to me and yes I expressed outrage about it to friends.
But your point is also a straw man. For the most part, there are still prohibitions on large gatherings of people. These protests have been blessed as an exception. Why? Because the government's hand was forced by political expediency. In essence, the government has failed to protect the people from themselves.
And let me flip the question on you: why do we need to protest so urgently now, during a global pandemic? Why can't it be postponed until after we've resolved that problem and can permit it to go about safely?
I'll answer that for you: BLM has found outsized effectiveness because of coronavirus. Because people have more time, and are feeling less economically secure, and are more emotionally vulnerable. They were better primed to respond to the movement and organizers are capitalizing on that at the direct expense of human lives, even if that isn't obvious to them.
Worst of all, history suggests that these protests and the consequent loss of life will buy Black people next to nothing. Categorically the wrong solution to a very complex problem.