I've done a bit of reading on the British pacifist front and it seemed that during the first stages of the war (up until about 1916) there was so much support that any opposition was confined to a few dusty corners of academia (one interesting account is is Bertrand Russell's autobiography).
Was there really so little opposition at the beginning of the First World War? Were the pacifist movements any different in France, Germany, Austro-Hungary or Russia? Did the pacifists deal any significant influence or did we have to wait later for conscription and war fatigue to kick in?
A great book on British anti-war movements leading up and during WW1 is "To End All Wars", by Adam Hochschild, who happens to be one of my favorite writers.
http://www.amazon.com/End-All-Wars-Rebellion-1914-1918/dp/B008PIC0T8
The reality is that the anti-war movements were very small, even if as the book relates some of the few involved were very prominent people.
Prior to World War 1 there was a great deal of free trade and travel and it was hoped by the pacifists that people were less nationalistic and that workers would see common cause and not want to fight each other. The pacifists in England attempted to reach out to like minded folk in Germany and rally "the workers" on both sides but it all came to nothing. In short the pacifists were not effective at all in the early stages of WW1, although on the English side did have some effect on mitigating executions for desertion and the like.