What is behind the fairly recent appearance of the "Cult of the Perpetually Offended"?

In my lifetime, when people disagreed with somebody’s opinion, they would say things like, “I don’t agree”, “You might want to check your facts” or even “You’re wrong about that”.
Now, often enough, people say “I am offended” when they hear a differing point of view. Speaking personally, this happens to me more on Fluther than in my normal “in person” life (I know that I am easy to disagree with, but offensive?).
Anyway, what is the official beginning of this trend?
Wouldn’t it be psychologically healthier, and less dramatic, to simply disagree, rather than be offended?