"But soldiers following orders to attack other soldiers is an honorable action. And fuck you for thinking otherwise."
This depends entirely on what the circumstances of the battle are, why it is fought, who is being attacked, the state of the battle, etc. etc.
Among soldiers there is an ethic of following orders no matter what because war needs to be simple for most involved for wars to be won. However, as SunZi pointed out, this does not absolve those involved of responsibility for actions they perpetrated.
So the idea that soldiers following orders to attack orders is always honorable is remarkably simplistic, just as it is simplistic to assume that honoring dead soldiers is an endorsement of war. It is not, it is contemplation of the act of giving up one's life for a cause.
I'm not aware if Anzac is tied to a specific campaign or war. Even if it was tied to an unjustified war, there is still:
1) cause to have a day of remembrance for those dead in the war
2) a large number of soldiers and civilians on both sides whose actions were not in themselves wrong, and whose sacrifices could be called honorable and deserving of honor, such as a day of commemoration
In sum: keep days like Memorial Day and Anzac because there are plenty of reasons to observe them regardless of how you feel about war.
I personally believe war is sometimes justified - the truest heroes are those who voluntarily fight in just wars - these people deserve special honor. But all dead deserve remembrance, and every war has its heroes on both sides who are morally blameless, even such incomprehensibly senseless wars as WWI.