There is an excellent argument for sentient robot soldiers and that is in the realm of collateral damage.
Today's "smart bombs" typically have a kill radius of 30m and a maim radius of 50m. This means that for one "surgical kill", dozens of non combatant deaths are likely (and do) occur.
A smart sentient robot could, instead, enter an area, only killing to gain access, before assassinating the intended target. There may be nearly zero non combatant deaths. There would also be a lot fewer maimed and no unnecessary infrastructure damage.
Surely, a war with sentient AIs would be more humane than todays so-called precision bombings?