There are two different groups of anti-war people: 1. People love peace and don't want war, but also they don't understand sometime war might be necessary 2. People who knew that specific war (Iraq war) would have very severe calculable and incalculable consequences that eventually hurt US.

Which group did you belong to?

As contrast let me tell you that they're also 2 groups of people outside of the US who supported the war: 1. Those shares the "values/belief" with US and saw the war would spread democracy and more importantly would deter dictator countries like China, and 2. Those who already knew the action would fail to prove democracy can be applied to any country, would weaken US so the world would be more balanced. History proved the 2nd group are correct.