Main line Christian denominations subscribe to the ecumenical creeds as the minimum beliefs required for being "Christian." Main line churches are thus able to differentiate between required Christian beliefs and optional denominational beliefs. Baptists do not have this ability and feel required to bad-mouth differing minor interpretations that main line Christians may ignore.
For example, my congregation invites anyone who is baptized Christian, and is a member of a Christian Church to join us at communion. Technically, Baptists Churches are not "Christian" but pragmatically most of our members don't know the difference.
many, if not MOST, main line churches/denominations today though have the creeds, the Bible, but no saving gospel/nor a Christ that saves, more into social agenda and social rights!
have the bible, but see it as just beimng "another" book!