Psalm 139: 21,22 WERNER BIBLE COMMENTARY ( hilighted sections and additions mine )
Speaking of Context:
He ( David ) described these wicked ones as speaking maliciously against God, lifting themselves up or arrogantly defying him to do evil. (See the Notes section for additional comments on verse 20.)
David hated those who hated YHWH, persons who defiantly disregarded his commands. The psalmist abhorred those who rose up against the Most High, rebelliously refusing to submit to his will. According to a Dead Sea scroll reading, the psalmist did not speak of loathing or abhorring them but referred to cutting himself off from any association with persons who rise up against God.
David's hatred for such godless ones was "complete," an emotion he felt to the ultimate degree. This is because he regarded YHWH's avowed enemies as also being his personal foes.
The psalmist's abhorrence for those who defied YHWH appears to have prompted him to look also at himself. He wanted to be sure that no trace of their disposition existed in him personally. Therefore, he wanted the Most High to examine him for the purpose of knowing his heart or his inmost self. He wanted YHWH to know more than his deeds and words, ( Lord, Lord, did we not perform powerful works in your name?!? ) and asked him to make a complete test of him so as to know his very "thoughts" ("paths," LXX).
David desired that YHWH would find no evil or injurious ("lawless," LXX) way in him, nothing that would lead him into wayward conduct. He wanted the Most High to guide him in the "eternal way" or in the way that would always be right or approved.
Again, Context ( we must consider the entirety of Psalm 139, not cherry-pick verses )
Notes on verse 20:
The last Hebrew word in verse 20 may either be a plural form of 'ir ("city," "town," or "village") or 'ar ("adversary"). According to the Septuagint, the meaning is "cities," and it reads, "They will take your cities in vanity." A number of translations take the Hebrew for "lift up" (nasá') to mean taking up God's name in vain as when swearing to a lie or speaking evil things against his name. "They say wicked things about you; they speak evil things against your name." (GNT, Second Edition) "Deceitfully they invoke your name; your foes swear faithless oaths." (NAB) "They speak of you with evil intent; your adversaries misuse your name." (NIV)
According to the context, David was not advocating hatred against anyone who disagreed with his decisions as King, even though he was divinely appointed, a claim no man or group of men can make today. David hated those who actually hated YHWH, while at the same time being fully aware of his own limitations and mistakes.
So considering the context, anyone misusing YHWH's name in a deceitful way, perhaps to gain power or wealth for themselves, or even to circumvent Christ's headship, would be enemies of Christianity and not worth associating with until such time as they humbled themselves and allowed YHWH to examine them, and show them the proper path. This would apply to all individuals as well as any Organized Religion and their leaders.