There are occasions when submissions are entirely removed and don't even retain the title or URL. I know this because I use hckrnews.com as my HN front page
Data scientist means someone who's had classes in stats and knows how to use software to analyze data. They don't cover how to run experiment and don't cover ethics
Yes, there is a way. You left them specifically opt in to it, you provide them disclosure documents of what's being tested, and you provide free access to mental health resources.
I disagree. If facebook is testing content like this then they explicitly know which content makes people sad. To manipulate someone's feed to push them stuff that knowingly makes them sad for the purpose of experimenting with someone's emotions, that is highly unethical to me.
There is a massive difference in studying and directing traffic to help make traffic flow better. The goal there is to improve driving for everyone. Facebook's goal is to intentionally make people unhappy for the sole purpose of making more money.