Failure of discernment of evil... Is it damning?

I have been thinking about this rampant problem that people cannot (or, at least, do not) discern evil; in particular that they impute good motivations even when evil is intended. 

I suppose most people would not regard this as a Bad Thing, and indeed might regard it as a sign of a Good Person that they assume other people are also Good... 

I find, however, that I can't believe it. I find that Good and evil are mostly about taking sides: the side of God and creation, or the side against them. So, a failure to discern evil is often - perhaps usually - in practice a matter of allying oneself with the side of evil, and against God. 

This would mean that a failure to discern evil - when one is in a position to do so - may be an act of self-damnation

But the consequences may compound the sin. This comes out in all sorts of ways. For example, people will often try to explain-away and excuse evil acts by saying they are actually well-motivated, or actually Doing Good. This they term 'giving the benefit of the doubt'.  

In particular, actual evil things happening in our own personal experience and to people that we love, are instead assigned to be motivated by remote, abstract, ideological Good, which we know only secondhand and from habitually- and systematically-dishonest sources such as government, the media and indeed large institutions of any kind.

Yet God will surely make it possible for us to know evil when it impacts upon us personally? And also know this from our own personal direct experience, common sense and capacity for reason (rather than needing to be told it by 'experts'? 

(Unlike those old-style communists who went to party meetings to be told who to support, and why (nowadays this job is done by the mass media). I think of those who were fanatical anti-Naziuntil 23 August 1939 when they discovered that Stalin had made a pact with Hitler. Presumably they then trooped obediently CP HQ to have it explained that - today - cooperation with fascists was Good...)

At the bottom line, I suspect that the discernment of evil is maybe the most important thing to do about evil; much more important than (supposedly) 'fighting' evil. We absolutely need to identify, and correctly, what and who is on the side of evil: who are evil-allied. And these evil-allied may well turn-out to be almost-everything, and almost-everybody - we should be prepared for that possibility. 

If I am right, this widespread and determined self-blinding to evil, the refusal to identify and acknowledge evil; may be one of the most prevalent and significant of our many modern sins.