I've been gradually realizing just how important it is to presume our ideological and political opponents to be motivated by pursuit of the good and true. Of course, in some cases the presumption is false, but likewise sometimes our co-partisans--and we ourselves--are motivated badly.
Here's a psychological advantage of making this presumption. If we lose out to our opponents (say, in the polis, in a department meeting, etc.), it's much less depressing when we see it as nonetheless a kind of victory for the true and the good--for we presume that the desire for the true and the good is what energized our opponents in their victory, what made them persevere, what made them win support.
It may seem not in keeping with a Christian view of this world as fallen to make this presumption. But at the same time, while this world is fallen, Christ's grace is widespread. And wherever people are moved by the true and the good, there is a likelihood that grace is at work. In fact, it is precisely the fact that the world is fallen that makes it likely that grace is at work where the pursuit of the true and the good energizes people.
None of this minimizes the importance of energetic disagreement when needed. If Fred and Sid disagree on which of two ropes to throw the drowning man, and Sid with great energy carries the day and throws the rotten rope to the drowning man, although Fred can see it as a kind of victory for the good in that Sid was being driven by the good, nonetheless the drowning man is likely to drown. So the presumption that our opponents are motivated rightly is fully compatible with resisting them respectfully to the best of our ability. Indeed, the very fact that Sid is pursuing the good is a reason for Fred resist Sid's mistaken choice of rope, so as to save Sid from an action that does not in fact achieve what Sid wants it to achieve.
Suppose it's granted that the presumption is helpful. But what justifies the presumption? Is it justified merely pragmatically? I don't think so. I think there is a general presumption that things are working rightly, a presumption that we should minimize the attribution of malfunction. (This general presumption may be what keeps us from scepticism, what makes it appropriate to trust in our senses and our fellows' testimony.) And it is a lesser defect to be wrong about the means than about the ends.