Phil notes that a spark/trigger can bring people together.
Was this in doubt? I don't think so.
People want to feel a sense of togetherness. It's easy to hop aboard a short-term opportunity to feel good. There is nothing to lose. You trade a few hours with a broom for a sense of achievement and togetherness. There is no social or physical risk there.
Compare this with the Turkish community in London that banded together and drove the rioters away.
The difference, as you can probably guess, is social capital. Not just bridging social capital, but bonding social capital. The London Turkish group feels a strong sense of community. They're a unique group in a different environment. They have strong social ties. They trusted each other. They came out for each other.
Whilst other business owners bemoaned the lack of police presence and watched their businesses get ransacked, the Turkish business owners made calls and saved their livelihoods.
Social capital is a powerful asset. But this isn't an advertisement of vigilantism. It's a reminder that when you want a group of people to do something that's hard or risky, a trigger wont do the job. A trigger didn't protect the dozens of business owners that lost their businesses. Hard, risky, and meaningful work requires a lot of social capital.
Social capital takes time to build. It needs to be carefully nurtured. It requires spending time introducing people to each other, encouraging people to interact, hosting events/activities, creating a shared history and building genuine friendships.
Most organizations, notably non-profits, do the process backwards. They pull the trigger first then try to build the social capital. That doesn't work. You need to build the social capital first then pull the trigger.
If you want people to take a few easy actions, then a good trigger is all you need. Most viral waves that sweep across the internet are built upon a strong trigger. If you want people to band together to do something that's hard, risky and meaningful, you need social capital. That takes far more time and effort.