Prior to the recent protests, the US seemed to be making some progress on controlling coronavirus, with an r0 of probably around 0.9, a slowly declining number of cases, and many states starting to ease lockdown. In particular, restrictions on large gatherings helped significantly slow the spread, because they reduce both the number of infected people who can spread it and the number of new people who can become infected. One (BERI funded!) study suggested that banning large gatherings reduced r0 by around 28%.
Unfortunately, protests seem in many ways ideal for spreading the disease. They involve a large number of people in a relatively small area for an extended period of time. Even protests which were advertised as being socially distanced often do not end up that way. While many people wear masks, photos of protests make clear that many do not, and those that are are often using cloth masks that are significantly less effective than surgical or n95s in the face of repeated exposure. Additionally, protests often involve people shouting or chanting, which cause infectious droplets to be released from people's mouths. Exposure to tear gas can apparently also increase susceptibility, as well as cramped indoor conditions for those arrested.
It's hard to estimate how many new cases will be caused by the protests, because there doesn’t seem to be good statistics on the number of people at protests, so we can't model the physical dynamics easily. A simple method would be to assume we have lost the benefits of the ban on large gatherings over the last week or so. On the one hand, this may be an over-estimate, because fortunately most people continue to socially distance, and protests take place mainly outside. On the other hand, protesters are actively seeking out (encouraging others to seek out) boisterous large gatherings in a way they were not pre-March, which could make things even worse. On net I suspect it may under-estimate the incremental spread, but given the paucity of other statistics we will use it as our central scenario.
If the r0 was around 0.9 before, this suggests the protests might have temporarily increased it to around 1.25, and hopefully it will quickly return to 0.9 after the protests end. Even if we assume no chain infections during the protest - so no-one who has been infected at a protest goes on to infect another protester - this means the next step in disease prevalence would be a 25% increase instead of a 10% decrease. Unfortunately the exponential nature of infection means this will have a large impact. If you assume around 1% of the US was infected previously, had we stayed on the previous r0=0.9 we would end up with around 9% more of the population infected from here on before the disease was fully suppressed. In contrast, with this one-time step-up in r0, we will see around 12.5% of the population infected from here - an additional 3.5% of the population.
Assuming an IFR of around 0.66%, that's a change from around 190,000 deaths to more like 265,000. Protesters skew younger than average, suggesting that this IFR may be an over-estimate, but on the other hand, they are also disproportionately African American, who seem to be more susceptible to the disease, and the people they go on to infect will include older people.
So it seems quite plausible to me that the protests might cause around 75,000 thousand additional Americans to die of covid, including probably over 10,000 African Americans. Additionally, despite the massive reduction in international travel, there will probably be some spread to other countries, especially if they have copy-cat protests.
There is clearly a lot of uncertainty about this number - my guess is that the actual r0 impact may be higher and longer lasting, but the IFR may be lower. If r0 is sufficiently low the disease will be suppressed more quickly afterwards, potentially making these numbers significantly too high (if the r0 were as low as 0.7, the protests would only cause an incremental 20,000 deaths). If r0 is a little higher then these numbers will be a substantial under-estimate. On the other hand, if the r0 was sufficiently high then containment will inevitably fail, and almost everyone in the US will catch it regardless of protests!
However, it seems hard to avoid the conclusion that the incremental number of deaths is quite likely many thousands. (In contrast, the Washington Post estimated that US police killed 41 unarmed people in 2019, of which 10 were black.)
My guess is that the indirect and statistical nature of these deaths makes people less sensitive to them. Probably if they were more emotionally salient, many protesters would not be willing to so endanger their lives.
As a result it seems to me that, even ignoring injuries and fatalities directly incurred during the protests, and the damage caused by associated looting, that the protests are quite bad, and it would be good if instead people stayed home to save lives and protect their local health systems.