Earlier quoted context omitted.
How do you distinguish between unethical science and A/B testing, or even just 'We changed our product, then didn't like the results, and changed it back?'
There is at least a dense 50 years of research and writing on the topic of scientific ethics, it's a bit naive to pop into a thread and ask, "so what's the deeeeaaaal with human experimentation?"
Concrete example: I am in the process of trying to hire people right now. I'm not sure what the exact best way to do that is, so I vary how I interview over time and see how well it seems to work. I record what happens in a spreadsheet, and then later on I look at the 'data' to make some judgments.
Am I experimenting on my interviewees? Am I potentially harming them?
Well certainly if I ask question A in one interview, and question A' in another, and question A' is harder and I don't pass that person, then one might be tempted to argue that maybe that person would've done better on question A; therefore, I've harmed someone by 'experimenting' and making it harder for them to get a job. Rejecting someone can certainly make them depressed.
In principle this is no different from A/B testing an interview process, using real live humans no less.
So do I personally have an ethical obligation to disclose to everyone I interview that I am conducting human experimentation on them? Or is the only difference in power and scale—I am just one person, but Facebook can A/B test on millions of people at once?