I don't think the fact that it's a hot topic is so relevant, the point to me is that Kara was not asking for feedback or discussion. Yes, she did open the topic up for discussion by posting it publically, but ultimately she was posting a video that she liked onto her page, not starting a debate on a topic.
Honestly, I think that's too close to asking other people to be psychic.
If you post things on Facebook you can expect other people to read them and comment on them. If you post about controversial issues, you can expect people to post dissenting opinions. You can expect them to be polite, but if you don't want comments, then don't post it in the first place.