I think you have too much faith in humanity. It had never happened in Tanzania until recently. And I think you're right about them being initially unarmed, but most people do have guns at home.
I'm depending on Americans to have a limit to their willingness to harm other citizens.
I know that hasn't been much in evidence lately, and I know that American humans are no more special than any other humans.
But we're starting from a very different place than, e.g., Tanzania.
I predict reversion to the mean, not revolution. (It can be argued that what we're seeing right now is the reversion to the mean, which is a whole different cart of apples.)
In particular, the largest protests against American elections (in my life at least) have been populated by almost-certainly unarmed protesters.
And there are many other countries with strict gun laws (i.e. not the US) where police don't fire upon crowds for any reason.