And the problem of the anti-war movement is not now and never has been that too few people oppose the war. From October 2001 to the present there has always been more than enough opponents of the war to build a huge anti-war movement. (I believe there were never fewer than 10% in opposition.) The problem has always been that the people opposing the war have, for the most part, not believed that anything could be achieved through active opposition.
To build an anti-war movement we don't need to find more arguments against the war. All the arguments we need were available from 9/11 on. We need an approach that will persuade people that active opposition is possible. I'm not sure that such an approach exists.
Carrol