Let's talk about when it comes to our enemies as Christians, the Bible says;
-Matthew. 5:44 -But I tell you, love your enemies and pray for those who persecute you
-Luke 6:28 -Bless those who curse you, pray for those who mistreat you
You will do exactly as these scriptures say, and them your enemies will keep going and going and devising more strategies to plot your demise, to curse you differently, to make your life more miserable, they will bear false witness against you also, they will slander you more and a whole lot of unpleasant things.
So, what I want to know is; is it wrong to stop praying for them and blessing them but in turn fight back with scriptures like;
-Psalm 70:2 -May those who try to kill me be humiliated and put to shame. May those who take delight in my trouble be turned back in disgrace.
-Psalm 40:14 -Let those be put to shame and disappointed altogether who seek to snatch away my life; let those be turned back and brought to dishonor who delight in my hurt!
-Psalms 35:7-9 -So let sudden ruin come upon them! Let them be caught in the trap they set for me! Let them be destroyed in the pit they dug for me.
What’s the way?
There is an old saying that fits here:
Were it not for the Grace of God, so go I.
In Matthew 5:44, the Lord is reminding us of one very important fact. We should love our enemies! Why is this? For one, because God showed believers MERCY and FORGIVENESS even though we were enemies of God. Therefore, believers should follow our Heavenly Fathers example:
Mat 5:45-47 that ye may be sons of your Father who is in heaven: for he makes his sun to rise on the evil and the good, and sends rain on the just and the unjust. (46)
For if ye love them that love you, what reward have ye? do not even the publicans the same? (47)
And if ye salute your brethren only, what do ye more than others? do not even the Gentiles the same?
Secondly, let us not forget, that if God had not done a work in us, we would be exactly like the one you are calling an enemy. We were no better than they before God called us out and we are still no better than they, if we cannot love, forgive and pray for them.
However, as a believer, this does not mean that you have to stand there and be abused -
IF the cause is for Christ. If it is for your own revenge, that is a different story. You should be slow to anger, slow to speak and slow to act. After all, what have they injured? Your pride? You will survive.
In the cause of Christ, you should be fierce towards those who are spreading lies, quick to shun those who work evil and hate the things that God hates.
In regards to the Psalms you quoted in your post... Please note that the Psalmist was talking with God - who is the righteous Judge - and many of the things he was mentioning, were about the revealed will of God towards those who are unbelievers. They were not about things that the Psalmist himself was planning to do.
Finally, keep this in mind:
Rom 12:17 Render to no man evil for evil. Take thought for things honorable in the sight of all men.
Rom 12:18 If it be possible, as much as lies in you, be at peace with all men.
Rom 12:19 Avenge not yourselves, beloved, but give place unto the wrath of God: for it is written, Vengeance belongs unto me; I will recompense, says the Lord.
Rom 12:20 But if thine enemy hunger, feed him; if he thirst, give him to drink: for in so doing thou shalt heap coals of fire upon his head.
Rom 12:21 Be not overcome of evil, but overcome evil with good.