You want to know how the Overton window shifted from workers as humans, to workers as property? Look at laws around the telephone.
If you have a telephone on your desk, it is illegal for your employer to secretly listen into those calls. However, if you send an email, you employer has every right to secretly read them.
The only difference is, emails don’t exist in the 30s, but telephones did.
I always ponder from this perspective as well, think about the strength of laws regarding physical mail as well. Most of those privacy/tampering laws should have been applied to email from the get go.
Objective snapshot-in-time comparisons like this are fantastic. It's all too easy for the novelty of tech churn to serve as justification for the age-old authoritarian desire.
If you have a telephone on your desk, it is illegal for your employer to secretly listen into those calls. However, if you send an email, you employer has every right to secretly read them.
The only difference is, emails don’t exist in the 30s, but telephones did.