Social movements are critical agents of change that vary greatly in both tactics and popular support. Prior work shows that extreme protest tactics – actions that are highly counter-normative, disruptive, or harmful to others, including inflammatory rhetoric, blocking traffic, and damaging property – are effective for gaining publicity. However, we find across three experiments that extreme protest tactics decreased popular support for a given cause because they reduced feelings of identification with the movement. Though this effect obtained in tests of popular responses to extreme tactics used by animal rights, Black Lives Matter, and anti-Trump protests (Studies 1-3), we found that self-identified political activists were willing to use extreme tactics because they believed them to be effective for recruiting popular support (Studies 4a & 4b). The activist’s dilemma – wherein tactics that raise awareness also tend to reduce popular support – highlights a key challenge faced by social movements struggling to affect progressive change.