(1) Description of the pattern
By definition, this is "absence or suppression of passion, emotion, or excitement." When adding the social aspect to this, it creates a negative connotation. Not only is one absent of their own life's situations, they care even less about the situations of others-- even if they can do something about it. Social apathy is a desensitization of humane involvement where society is concerned.
(2) Why the pattern is good (i.e. bad)
Much like "Unacknowledged Privileges" this a great pattern of avoiding opportunistic callings. Whenever one comes upon a chance to make a difference in another person's life they can fall back on the fact that it is "not their problem."
(3) How it works
The belief that "you can't fight city hall" helps to ensure inaction.