From my limited information the MCAS code was primarily causing problems in association of incorrect readings by damaged sensors. Of course one could argue that this is an engineering failure because the MCAS failed to account for wrong sensor input but when you consider the legal implications of a MCAS fallback there is actually not much that can be done on the software side.
The MCAS is an optional component that reduces certification and training costs. It is definitively possible to fly the plane without accidents even with a disabled MCAS. So why can't the MCAS be turned off automatically when sensors fail? Because that changes the classification of the plane and therefore requires pilots to be certified for a new machine and receive new flight training for both MCAS and no MCAS modes.
If the software engineer was under a hippocratic oath then he would have to refuse to build the MCAS entirely but not because the idea of an MCAS is inherently unethical, no, he would have to refuse because the company he works at wants to use the MCAS for a non ethical purpose (namely operate and hide the existence of MCAS even when it is unsafe to do so).
This is basically a reverse audit but the software engineer has no authority conduct such an audit and even if he was allowed to, the business has no obligation to give him the necessary information to determine whether the MCAS will be used unethically.