Citizens were loyal to Rome. Soldiers were loyal to their commanders. If commanders wanted to launch rebellions, the soldiers would likely support them.
A commander who commands the loyalty of legions by convincing a handful of drone operators would be very dangerous for democracy.
I'm not making a values judgment here, just saying that they will absolutely be used in war as soon as it's feasible to do so. The only exception I could see is if the world managed to come together and sign a treaty explicitly banning the use of autonomous weapons, but it's hard for me to see that happening in the near future.
Edit: come to think of it, you could argue a landmine is a fully autonomous weapon already.
Honestly, even landmines could easily be considered fully autonomous weapons and they don't care if you're human or not.
Notably USA is not one of those signatories.
