Shutting down traffic. Vandalising property. Threatening or engaging in violence. While these forms of extreme protest might undercut public support for a movement, they're remarkably effective at raising awareness about social causes and placing pressure on the institutions that can act on them. So, what should activists do - refrain from highly disruptive protest to keep the public on their side or risk losing popular support by protesting in the extreme fashion likely to grab the attention of those in power? In a nutshell, that's the "activist's dilemma," the subject of a new paper by Robb Willer, a professor of organisational behaviour at Stanford Graduate School of Business.

Willer and two co-authors investigated the widespread claim that extreme protest actions - those viewed as "harmful to others, highly disruptive, or both" - erode public support for movements. Across six experiments focused on such movements as animal rights and anti-abortion to test this hypothesis, they found that extreme forms of protest lead to a drop in social identification with the various causes. This is of concern to activists because movements that lack popular support are unlikely to grow and could even face public opposition.

"The takeaway is not a simple one for activists," Willer says. "There's a reason we titled it 'The Activist's Dilemma.' Activists want to be relevant and noticed and adopt tactics toward that end, but at the same time, they want to build support in the general public - and it's just very hard to do both of those things at once."