The best thing a software union could do is refuse to build harmful technology.
My point is that this is a group activity. Ascribing the status of harm causing behaviors happens in aggregate. This is in contrast to workplace decision making which happens hierarchically. Democracy is a superior version of decision making right? Why should that idea cease to exist the moment someone steps into the workplace? Who has an interest in perpetuating the myth that workplace democracy is untenable? We run whole countries with the input of citizens, surely that could scale down to a workplace, right?
Not always, no. Everything has nuance and context. For example, would you like democracy and voting in the emergency room? While I don't agree with it, China has demonstrated interesting results from non-democratic decision making. Certainly direct democracy does not scale well and would be a terrible idea at out present moment.
Is the country really run with the input of the citizens? What are politicians optimizing for? What are the contents of the policies being passed and what are they based on? Who's actually writing the majority of that? Do all employees have the ability and context to make informed input or decisions? Are there any decisions which will make all people happy? Do all people consider the same acts harmful?
What if we think about workplace requirements for vaccines? Does your opinion on employee option to not consent remain?
Perhaps try to avoid treating the other person as an adversary when they don't agree with you
Most people don't have the kind of eff-thou money, which is why OP asked his question conditioning on unionization.
Workers: We don't want to do labor unless it is tied to more pay.
Employer: No, we want you to do more work with the same pay.
Workers: Ok, we will do less work then.
Employer: Ok, work longer hours then.
It sounds a lot like what we already have right now. There are better questions than "what about time-theft?"
The rest is noise