Qantas have done the right thing. To inconvenience literally 1000's of passengers (keeping in mind that all flights are interlinked) - and to disrupt the smooth operation of an airport and commercial flying operations - is the aviation equivalent of a builders labourers strike organised to commence, right as a major concrete pour starts.
These QF pax definitely set out to cause strife and disruption, and were obviously intent on inflicting their minority view on the majority via that major disruption.
The fact that these people are associated with a group involved in social justice issues is merely reinforcement of general opinion that they intended to create disruption as regards the deportation of the individual, and to focus media attention on the deportation.
As well-stated by a previous poster, these social justice groups and individuals seek to impose their minority views on the majority, and to override and disrupt substantial legally-approved and legislated immigration processes that are lengthy and considered.