The Holy is transparent, whereas the unholy is opaque.
And that which is in the middle, which can go either way, is neutral.
This is the discussion of a couple of Rabbis at this weekly show.
I think the idea of gemstones (or stones in general) wonderfully explains this concept.
A beautifully cut gem, like a diamond or an aquamarine, gives so much pleasure to our eyes because it is so transparent. The more transparent, the more expensive. What gives it this transparency is the work that went into making it so faceted. Holiness requires work to achieve its perfect transparency.
Those uncut gemstones, which have the potential to be worked on to be transparent (cabochons for the precious stones, and others like turquoise or lapis lazuli) are less attractive to us because of their middle-ground. But, we still desire them because we see the potential in them.
Yet, sometimes what looks like a potential turquoise can end up looking like an opaque pebble. We are least attracted to this pebble, and most likely to discard it at some point.
And that is exactly what the judicious Rabbis say. The opaque requires no judgment. They call it evil at one point, but prefer in the end to describe it as something which wouldn't bring us closer to God, and therefore something to be discarded.
On a more practical level, evil (the opaque) always leaves us questioning and probing (why, how what, etc...) whereas we marvel at the clarity of Holiness.
But, rather than judge it with our limited capacity, it is better to leave the opaque aside, and concentrate instead on the Holiness that is in front of us.