"I can obviously not imagine life as a black person in America" you could have stopped there on that matter, being that you are white and in the UK.
Lots of groups are trying to fan the flames...there have been no other flames to fan.
If black men had showed up with automatic weapons they would have been arrested, you cannot own and automatic weapon here...tell the rest of the world, who seems to be very unclear about the gun laws here, that none of the weapons they see Americans walking around with are automatic weapons. In answer to the main point of your question, I think they should have showed up armed right from the start. A show of equal force tends to keep the other side from doing anything aggressive...like firing tears gas into crowds of people.
Although I am a white Brit I have known plenty of black people and some of them suffered harassment by police. A racist police force is bad for society, but some of those attracted to that job will hold such views.
I am showing my ignorance of guns in general. I saw someone was arrested for use of a deadly weapon when they threw a tear gas grenade back at the police. How cynical is that?
I think peaceful protest is a powerful weapon. It carries risks as MLK and Ghandi found out.