Why do we push away, or attack, or push out, others who differ in belief from us?
Christena Cleveland wrote an excellent piece about a recent book by Rob Bell and subsequent division and fighting of “pro” and “anti” camps of other Christians (see http://recoveringevangelical.com/2011/03/why-love-rarely-wins/).
On the second point, I see an anthropological reality (and would point to Miroslav Volf's excellent book, Exclusion and Embrace) - it has to do with the creation of group identity, and with in-group (“us”) / out-group (“them”) dynamics. We define our group with certain boundaries (in the case of evangelicals, those boundaries tend to be marked by specific beliefs), and build walls, and push away (or out) anyone who blurs the line, or who claims to be “in” but doesn't respect our boundary markers or in-group characteristics. The wall-building phenomena is particularly evident these days between Christians and Muslims. It's sad, though, that the dynamic is also strongly at work within Christian circles, in what seems to be an ongoing effort by some to “purge” the group of those who don't fit in (and it seems to me, sadly, that evangelicals are the worst).
Personally, I think evangelicals err in defining Christian faith cognitively more than relationally, affectively or behaviorally. In my reading of the New Testament, Jesus teaches the centrality of relationship, with himself and with others. He teaches that he saves us - through relationship, and clearly indicated by our emotional (affective) and behavioral response to him (e.g., do we love him, obey him, follow him, cling to him, “feed” on him, etc.). And Jesus also taught that our relationship to him creates relationship with all others who love him and are in relationship with him (and also with all other human beings). The second great commandment, according to Jesus, is to “love our neighbor as ourselves”; and don't forget that he illustrated the nature of loving neighbor with the example of a Samaritan, someone who the Jews despised as racial/ethnic bastards and having a distorted and false religion. If his followers are to love even those who they naturally despise, how much more should they love others who are following Jesus?
It seems that we are failing to love, and to me, this is an almost total failure of our faith in Jesus, given the centrality of the love command.