Combining unethical and necessary defeats the point of identifying some things as unethical: if you're going to do them anyways, why bother calling them wrong? The motivation behind bringing ethics into the workplace is that broader human interests are that engineers and other front-liners (operators, doctors, technicians, soldiers) should refuse to do things that are excessively bad. If you think they should just suck it up and get the job done, then don't bin the job you want them to do in with other things that they clearly shouldn't.

It needs to be considered acceptable to tell your boss no on ethical grounds.

To make this concrete, we want there to be one bin for "putting live viral payloads in to vaccines destined for a foreign country," and another bin for "annoying shoppers with eye-level advertisements," and maybe another bin for "improving the efficiency of infrastructure." Ideally, irrespective of where the profit motives lied it would be impossible to recruit anybody for sufficiently nefarious purposes, with the recruitment difficulty scaling with how much harm they knew they were going to do to the world.