The concept has gotten a lot of bad rep on the Internet lately, mainly through the exposure to Reddit. It's treated among many as something only weirdos or morally-uptight assholes do to, presumably, boost their self-esteem. This is odd - and this is wrong.
Seems to me that the modern world promotes self-exclusionary behavior. It very obviously does in Russia, but I think it's not unique to the country: it's a manner of the self-righteous countries, and the US is among them. People under such paradigm mostly aren't inclined to stand up for an unfamiliar person abused in public; an unfortunate many won't stand up for those they know, as well. They would rather tell themselves that it's none of their business or that they better not involve themselves for one reason or another: they might get hurt, they have people to care about, they don't want to be seen as someone bad and so on, and so forth.
They would be right: it is none of their business. They just happen to witness an injustice, come upon it without willing to or looking for it as if it's their mission to do so.
That reminds me of the wonderful speech Reverend Martin Niemöller gave during the Second World War (and one of its poetic versions):
I did not speak out;
As I was not a communist.
When they locked up the social democrats,
I did not speak out;
I was not a social democrat.
When they came for the trade unionists,
I did not speak out;
As I was not a trade unionist.
When they came for the Jews,
I did not speak out;
As I was not a Jew.
When they came for me,
there was no one left to speak out.
You don't have to speak up; you must. You do, because when time comes for you to be wronged by someone, you'd want someone else to speak up on your behalf. You do, because it's the right thing to do; the bother on your conscience when you don't tells you so. You do, because we each are flesh and blood of each other.
It's difficult to persecute moral crimes. Law enforcement in many countries doesn't do that often. It is then that the human power of the society is to be acted upon: we, each, make society as it is. One acting justly is almost nothing; many is a force to be reckoned with.