Lets face it, we all are evangelists for something. Some may not like the word "evangelism" or identify as "evangelical" because of a particular social stigma, but even the most liberal atheist is evangelical for something.
Everyone is an evangelist. From locavores to free market capitalists. From the 99% to the 1%. From the soccer mom to the marathon runner. Everyone is an evangelist.
Liberal and mainline Christians need to get over being afraid of being evangelistic.
Evangelism is not something that just one sliver of Christianity has a monopoly on. While we sit back and remain distant and silent on evangelism there is a small group of people taking a term of Good News and turn it into a battering ram of bad news.
I do not think that you have to be a Christian to be a good person, but I do think that everyone needs to be apart of a spiritual community to be whole.
Evangelism in not about getting sinners to be saved, but about working with others to ensure we are all made whole.