I have a better idea for controlling prison costs (at least in the US): let the non-violent drug offenders (~20% of total offenders) out of prison, and don't pu

I have a better idea for controlling prison costs (at least in the US): let the non-violent drug offenders (~20% of total offenders) out of prison, and don't put them there in the first place. When ideas like the above get completely shut down by the prison lobby, imagine their reaction to "let's replace prison guards with robots lol!!" Broken prison systems aside, can anybody point out cases of humans being replaced by robots being cheaper than just paying a human to do it? I know for things like manufacturing this makes sense (so machines building machines) but as far as machines interfacing with humans, it seems the cost would be higher.