If you're sitting in an office twiddling your thumbs for 4 hours a day you're not defrauding your employer.
If you're at home working a second job (or mowing your lawn) for 4 hours a day then you're committing fraud and violating your contract with your employer.
Fundamentally it's a legal issue about fraud.
If you want remote work then you need a very different kind of employment contract. (One that specifies concrete deliverables, not time owed.)
So you just want to lord over the minions, even if they're not actually doing anything for half the day? You don't actually care about productivity, you just care that you can exert your power over them and have them rot in a cubicle doing nothing, even if they were doing equal amounts of work in both situations.
Complaining that they're not properly using the time they bought is like claiming you can joyride your neighbor's expensive sports car because he's not using it most of the time anyways.
We're a remote heavy company and we don't have that type of contract, and it all works really well.
So no, you don't need it.
We are now past that point where everyone plays nice working remotely.
And if there are people working 4 hours a day remotely, how productive do you think those same people are just because they're sat in an office?
Nutshell: I think this is a nonsense argument.