Foster-Miller (among others) has been working on an autonomous version of it's "Talon" remotely-operated small tracked vehicle since the Oughties. When your enemy arrays autonomous infantry robots against you, common sense dictates you don't meet them with flesh-and-blood soldiers.
You do realize "Terminator" wasn't a documentary, don't you?
It takes longer to grow the experience an infantryman or a tanker or an mortarman or a fighter pilot needs to be combat-effective than it would take to build a robot to perform his role. Robots need no training and you don't have to write a letter to its parents if it should get destroyed.