No - it’s not ethical.
Very little evil is actually a direct result of evil people doing evil things. The vast majority of it comes to be through ordinary people doing banal things - things that, like building weapons, are questionable at best, but that they excuse because it’s “out of my control.”
The thing is that it’s not out of their control. Yes - if one individual makes the decision to not take part, that’s not going to have much of an effect, but if every person who feels the same way makes that same choice, that absolutely WILL have an effect.
And there’s only one way to make it so that every person who feels the same way makes that choice, and that’s for each one of them, individually, to look past that “it’s out of my control” bullshit excuse and go ahead and do it.
Everything on any significant scale is out of individual control. Individuals just possess a very limited amount of control over affairs on a national, much less global, scale. But that’s really entirely beside the point. The point is how you choose to exercise the small amount of control you have. Will you use it for good, or for evil?
And some number of those workers have the exact same opinion that you do - they’re opposed, but they don’t think they can make a difference.
And if all of you stopped waiting around for some charismatic leader to tell you what to do and just went ahead and made the choice you prefer, you would make a difference.