At least one preacher, Greg Laurie, has said it: To not share the Gospel is a Sin of Omission.
I have often seen a big difference between the Southern Bible belt and the American East. The largely evangelical populated south loves to preach to others - though often in a manner assuming others are worse in faith; As for the East such as New York, Boston, etc., Christians are mixed with different denominations, and catholics, eastern orthodox, christian cults, muslims, perhaps even the influence of the Jews, that it is not surprising that many Christians - especially of the "traditional" groups, intentionally believe that they are not responsible to preach.
So there we have the two groups. I'm not proud of any particular group, because many evangelicals do not discern the line between the duty to preach and salvation not by preaching but by personal conviction; while the "Europian style" Christians believe more on moral and the less chance to sin if they don't touch others.
Consequently, the South gets jealous easily when they see others better than themselves while the East just gradually slips into oblivion as other faiths take ground.