I don't understand this "against America thing". How can it be- in what way can it be- called 'Anti-America'?

As for whether it will make a difference: Definitely. Maybe it won't put a stop to the war plans, maybe it won't change the Bushwhackers' minds one iota, maybe tempers will flare and people will come down hard on one side of the issue or the other but it's kind of like one's vote. One vote doesn't usually make a difference to the outcome- but it does make a difference to the voter who put him/herself on record as to what developments are desired.