I agree with your main claim that the protests will cause more deaths than they save, but I disagree with your estimate of caused deaths by at least an order of magnitude.′
The estimated change in reproduction number is not compelling. Firstly, the largest protest in American history had attendance of 3*10^6, or one in a hundred Americans. So assuming this protest is tied for most attended in US history, and other Americans behave the same, the protestors must each have an R of 30 to bring our average R from .9 to 1.25. That is 10 times the pre-SD reproduction number. Assuming the protestors have an R of 3 or 4 seems reasonable to me. Now that we know much transmission is from speaking, 10 would be the upper limit of my 95% CI. Assuming an R of the 3, reduce the estimate to 10%
Also the protests are short relative to the time a person is contagious. I doubt the protests will maintain attendance in the millions for more than two days, which is less than people are typically contagious. Therefore their influence on our effective reproduction number will be less than you estimate. Seems like people are contagious for at least 4 days, so call that a reduction by half. So reduce the estimate by a further 50%.
So I would reduce your estimate from 75,000 to 4,000. Which is still a lot. More than my expected benefit from the protests by movement building.
Democracies did not exist in the premodern world for one main reason; they were bad at war. Revolutions and republics did form in the Medieval period, particularly in capital-intensive trade hubs like Northern Italy and Northern Germany. However, most were quickly crushed under a wave of poorly armed peasant-soldiers from the coercive states next door.
A major reason for democracies rise in the 17th-21st centuries because democracies suddenly became much better at warfare than all other systems, and have maintained this advantage ever since. The first state to create a democratic nation-state and harness it to war was the Dutch in the Dutch revolt, who shocked Europe by defeating the Habsburg Empire. Shortly afterward Britain formed a democracy-nation hybrid who set the standard for military power. All major world wars since have been resounding Democratic victories., from the War of Jenkin’s Ear to the Cold War. The main advantages of the democratic system are
Modern democracies had both large populations and property rights for capital, combining the two great advantages of previous state forms. Some autocracies have greatly improved their ability to accumulate capital to close this gap (Fascist Italy, China, Soviet Union).
Leaders pay a higher cost for defeat
Democracies can more credibly issue bonds (democratic advantage has faded over time)
Democracies rarely have to coup proof (divide and purge the military to prevent coups)
This advantage should be completely irrelevant going forward. China and Russia may democratize, giving the democracies a clean sweep of the security council powers. But the democracies are already at maximum influence in many stable anocracies like Morocco and Jordan.