Cornellia has summed up the role of the Druids nicely; that’s the point I was trying to make, but much more concisely put. (Though I don’t know that human sacrifice was JUST an excuse; it tended to make Romans rather nervous, perhaps because it wasn’t that far in their own past.)

I don’t know that one can say that the actions in Judea were against a religious group. Both times the people were in open revolt (as Pectinarius notes). Their reasons for revolt may have been religiously motivated (at least partially), but it wasn’t religion that the Romans were after. The Jews got a special break on the matter of the state religion thanks to the help they gave Caesar when he was besieged in Alexandria. Of course, they were also a client kingdom which put a layer of insulation between them and the Roman state, too. Once things changed they could always point to legal precedent, which was usually an argument killer in Rome.

The Druids had no such precedent and they were the driving force behind resistance to Rome. As the guardians of Celtic culture, they did their best to argue against the Romanization of their people. Sometimes those arguments took the form of armed violence. (There is a temptation to draw a parallel with current events, but I shall refrain.) Here too, the actions of the Romans may not have been directed against religion, per se. Perhaps if there had been a druidic faction that was willing to get along with Rome, the Romans might have engineered a coup and reorganized things to their liking.