Social media can be both a blessing and a curse.
When used for good things, social media is perhaps the most powerful tool in the world. Social movements (#BlackLivesMatter, #BringBackOurGirls, are just two examples), awareness campaigns (#FreeRaifBadawi, for example), watchdog-esque behaviour (recording of police brutalities, for example), are some of the best instances of social media being used for good.
The instances in which social media is used for awful things are plentiful as well - vigilante justice, executed because of a rumour started on social media, or the spread of misinformation, is one example. It also provides a vehicle for people's anger and a platform for them to parade their ignorance in some cases.
I only use Facebook regularly, Twitter sort-of-regularly, and Instagram and Google Plus less-sparingly, I don't have a Tumblr account, or any other form of social media (FourSquare, etc).
In short, it is what you make of it. You can choose to use it however you please.
Though none of this addresses your question, so I'll try and do that. And the answer to the first question is largely, "It depends." It depends on whether or not the picture, or video, in question is that of a man being shot by a police officer as he was running away, that of police officers choking a man to death, that of Raif Badawi who was being 'lashed' for the awful crime of being a writer and an activist and criticising Islam in Saudi Arabia. In that case, the video brought to light the horrors of the Saudi Arabian regime. In that case, then it is a very big deal.
To your second point, things are sacred and secret if you choose them to be so. Decency and integrity are still there. It really comes back to how one uses social media.
