This isn't just a comics phenomenon; all entertainment media have seen increased prominence of anti-heroes (in great part due to the relaxation of censorship and S&P that allows writers more latitude in what they can depict).
I think that this wikipedia article
is pretty straightforward in its description of the anit-hero and the concepts origins as well as its place in comics.
With regard to the thread topic, I believe that only the first fifteen minutes of The Cage are canonical and all Star Trek that follows/(predates?) deserves to be wiped from existence and destroyed my childhood memories of the show.