Their country did not have the authority to order them into conflict.They chose to serve their country in its armed forces and made that commitment before they were ordered to go into conflict. They trusted the body politic. Any failure isn't theirs. I am pretty sure they wouldn't care that you don't approve.
Governments are too powerful to be held accountable. They've been arrogating authority and fomenting endless wars for thousands of years. In this they're no different from large street gangs, or Hamas, or Daesh.Sovereign nations have the power to take the lives of others just as societies and individuals do and the onus of being held accountable for doing so. If you feel so strongly that America was wrong then you should show ethical integrity by leaving it.
Commitment or loyalty to an individual, organization or government is hazardous. Governments change. A government that seems benevolent today may choose to invade Poland or Ukraine tomorrow.
A person has personal responsibility for his actions. Ethical integrity is best assured by staying unaffiliated and choosing moral actions.
How would leaving America be showing ethical integrity?