Community opposition to locally unwanted development is not inherently problematic, but it can be destructive where conflict between proponents and objectors escalates. This paper relates mixed-methods findings from a Sydney case-study where opposition to planned affordable housing projects was widespread but uneven. Five factors are identified that escalated individual opposition campaigns in this case: public notification procedures; sense of injustice; prejudice; strong campaign leadership; and the involvement of politicians. We argue that these factors will likely also escalate opposition to the planned development of other forms of critical social infrastructure, and that an understanding of them can help minimise destructive conflicts between proponents and host communities.