The same occurred in WWII. The two goals are not mutually exclusive.
Not mutually exclusive, but saving innocent lives is a consequence of asserting US interests with the US military, not a purpose.
What your son did and mine are doing by promoting US interests may have resulted in saving innocent lives. Saving innocent lives alone is not to be confused with the definition of what constitutes US interests outside of promoting a defined US interest.
Your son's primary mission, as is the mission of my own sons', is to protect US interests. Period. Saving innocent people is often the outcome and consequence of US intervention, but never is it a solely defined purpose.
If a COC attempts to use US military assets solely for the purpose of saving innocent non-American citizens' lives absent a direct US interest for doing so, he has mis-appropriated those resources for a purpose not authorized in the Constitution.
The US military is not a global social program which exists to alleviate the suffering of the world's tyrrany-oppressed peoples.