Isn't this just what every media company has done since the beginning of time? You think the news companies don't select their stories based on the same concept? And I'm pretty sure you would get approval to do something similar to animals given that you can get approval to actually feed them drugs and see how that affects their behavior.
I can speak to the types of experiments done, and media companies never had the same degree of ability, data or talent.
Even something benign and commonplace like A/B testing, was not possible given a physical newspaper.
Can you provide evidence that [non-social] media companies have performed research specifically to see if they can make people sadder, similar to what was described above?