This is a really well-written summary. I especially liked your pointing out that, while it's harder for one protester to make a difference than one voter, demonstrators can *multiply their own influence* (by dressing in costume, writing a clever sign, or doing something else to draw media attention).

Voting is has a rare property among activities; people who do it are forced into a state of absolute equality. Protesting, like most activities, runs on something like the Pareto Principle; the most effective protesters probably have a lot more influence than other protesters.