We really do have a selective memory, don't we? And I mean all of us, no matter where we stand on any issue. We tend to only remember the past in a way that supports our foregone conclusions about the present.
That's why we need two things: Each other (especially those who disagree), and the Holy Spirit. Each other because we bring each other face-to-face with another viewpoint. And the Holy Spirit so we don't kill the other before listening to them!