Because motivation is primary in morality, discernment of the motivation of others is essential; we absolutely must be judgmental.
If we refuse to judge, we will not be able to choose validly who is motivated by good, and who by evil. We will not be able to pick the right side (the side of right).
We will not know whether we are working on the side of God, or of the devil.
(This is especially important here-and-now - when the side of evil is so dominant in the world; when evil dominates all large and powerful human institutions.)
Note: This is why one-ness teachings usually end-up preaching evil in modern Western conditions: because they argue against discernment and judgment. They try to convince people that we ought not to discern beautiful from ugly, virtuous from wicked, truth from lies... on the basis that all such are merely superficial illusions (maya). From a Christian perspective, this means that adherents of one-ness in practice go with the dominant flow: and thereby (albeit flaccidly) support leftist, totalitarian materialism, and fashionable 'causes'. This (under current conditions) generally means aligning-with the side of evil; neglecting to discover and work-with divine creation. Furthermore, anti-discernment, anti-judgment leads to enfeeblement of motivation generally; since it is not worth the effort of doing one thing rather than another - or some-thing rather than no-thing.