I think I would be OK with what they did, bar the repeated applications (once by one of the captain or CSM is fine - preferably from the CSM so they can say both "buckle up" and "service is off for now" at the same time - plus of course all crew members checking for action). Sure, I'd lose sleep, but better than getting hurt in turbulence.
People are going to be woken up anyway if they don't have their seat belts fastened because the FAs will tell them to do so. For those that have the sensibility to buckle up when seated, it's only a minor disturbance (read: assuming a rational, reasonable PA transmission - you may be excepted).
For the terminally stupid
Don't joke. You'd be surprised how many air passengers leave their common sense back at home. That's why we live in such a litigious society these days. For companies to do supposedly obvious things, it's a small sacrifice for legal peace of mind.