I doubt the engineers who signed off on MCAS recognized it as an 'unsafe system'. I've never met an engineer - or even a manager - who would knowingly sign off on something they believed was 'unsafe'. As Safetypee pointed out, much of the issue with MCAS was related to subjective judgements - especially the assumptions of pilot reactions and reaction times. Those judgements in turn lead to the assessment that an MCAS malfunction would be no worse than 'MAJOR' - systems with 'MAJOR' failure consequences don't get close scrutiny because they are not judged to be that serious.
Shortly after the Ethiopian crash, I was at a fancy dinner event where I happened to sit with a group of retired Alaska Airlines 737 pilots. To a man, they agreed that the
first thing they'd do if the stab trim started doing something they didn't understand would be to turn it off. But these were old school, high time pilots - some experience dating back to the
737-100/200 series aircraft - and not taking account that at the same time the stick shaker and other alarms would be going off.