I mean, I don't really understand the 'feeling inadequate because of my cousin's baby pictures' thing. I mean, I am happy for them, but that isn't the life I want, so I don't feel bad that I don't have it. Alternately, I could be less jealous than most people, but let's run with the more realistic first reason.
For me, the problem with social media is a fundamental lack of self control; I get into 'someone is wrong on the internet' discussions, and for me, those are the 'addictive but not pleasant' aspects of social media. For me, a conversation is not fun if we aren't arguing in good faith ; if we can't acknowledge one another's good points and rhetorical flourishes, it is just not fun, and I end up feeling frustrated and rejected. The unhealthy part is that I feel the discussion is unfinished, and walking away takes a tremendous act of will, and even then, my mind keeps coming back to the conversation.
I hope it is just a matter of practice; I mostly have left other mediums with these sorts of unfufilling conversations, or at least learned to restrain myself from participating in the most obviously unproductive conversations.
I think the big difference with social media is largely cultural; lots of people are there who lack a background in early internet culture or academic culture, and our shared vocabulary doesn't run much past "you are wrong " and there isn't the social pressure to be civil like we have here, or to be smart, like there was in the heyday of kuro5hin.