'hate the sin but love the sinner' is a manmade phrase. Of course, because the born-again believer has the Holy Spirit, he then does love some or many who are sinners without Christ. But he doesn't love all sinners, and is not required to.
What verse or verses are you addressing? If, as you say, discernment is needed, then loving ones enemies is not a blanket statement covering all our enemies.
Stranger
Jesus forewarned us not to be offended by the kind of enemies that thinks they are doing God's service by killing us;
John 16:1These things have I spoken unto you, that ye should not be offended. 2 They shall put you out of the synagogues: yea, the time cometh, that whosoever killeth you will think that he doeth God service. 3 And these things will they do unto you, because they have not known the Father, nor me.
He even cites a very broad general statement in how we are to respond to enemies in spite of their actions.
Matthew 5:43 Ye have heard that it hath been said, Thou shalt love thy neighbour, and hate thine enemy. 44 But I say unto you, Love your enemies, bless them that curse you, do good to them that hate you, and pray for them which despitefully use you, and persecute you; 45 That ye may be the children of your Father which is in heaven: for he maketh his sun to rise on the evil and on the good, and sendeth rain on the just and on the unjust. 46 For if ye love them which 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 publicans so? 48 Be ye therefore perfect, even as your Father which is in heaven is perfect.
There is no way you and I can do that by our efforts or will power which is why I rely on Him to help me to love my enemies by supplying the love and the longsuffering to love my enemies.
Paul mentions the end purpose for suffering those afflictions;
1 Timothy 1:15 This is a faithful saying, and worthy of all acceptation, that Christ Jesus came into the world to save sinners; of whom I am chief. 16 Howbeit for this cause I obtained mercy, that in me first Jesus Christ might shew forth all longsuffering, for a pattern to them which should hereafter believe on him to life everlasting.
Peter cites the example of Christ Whom we can look to in order to help us suffer grief wrongfully in this life.
1 Peter 2:19 For this is thankworthy, if a man for conscience toward God endure grief, suffering wrongfully. 20 For what glory is it, if, when ye be buffeted for your faults, ye shall take it patiently? but if, when ye do well, and suffer for it, ye take it patiently, this is acceptable with God. 21 For even hereunto were ye called: because Christ also suffered for us, leaving us an example, that ye should follow his steps: 22 Who did no sin, neither was guile found in his mouth: 23 Who, when he was reviled, reviled not again; when he suffered, he threatened not; but committed himself to him that judgeth righteously: 24 Who his own self bare our sins in his own body on the tree, that we, being dead to sins, should live unto righteousness: by whose stripes ye were healed. 25 For ye were as sheep going astray; but are now returned unto the Shepherd and Bishop of your souls.
I can't see myself not returning revile for revile or not seeking vengeance on those whom hard me or even defraud me, but He has done it; He has carried me through many situations where teh devil often times taunt me to look back on it, get mad and hateful, and imagine wrath and malice for which I turn to Him to help me stop thinking about it and to forgive them as He had done while on the cross because they know not what they do.
It is b.s. in asking believers to love their enemies by their merit and will power, but not when we lean on Him to give us the love ( which is a fruit of the Spirit ) we need and His help to love our enemies. Paul did point out that there will be situations when it is impossible to love our enemies, from which we can only stay away from them but lean on Him to love them enough to pray for them in living peaceably with all men.
Romans 12:17 Recompense to no man evil for evil. Provide things honest in the sight of all men. 18 If it be possible, as much as lieth in you, live peaceably with all men. 19 Dearly beloved, avenge not yourselves, but rather give place unto wrath: for it is written, Vengeance is mine; I will repay, saith the Lord. 20 Therefore if thine enemy hunger, feed him; if he thirst, give him drink: for in so doing thou shalt heap coals of fire on his head. 21 Be not overcome of evil, but overcome evil with good.
Now if we were to apply His words to the devil since he is our enemy, I do not believe that was whom His message was for since he cannot be redeemed.
I will point out that during the great tribulation, those with the mark of the beast are damned to the lake of fire no matter what, and although I am certain that the saints are not to take vengeance on them, I would think they would not be loving those enemies, but not exactly hating them either because that would just tempt them to kill the ones with the mark of the beast.
Revelation 13:9 If any man have an ear, let him hear. 10 He that leadeth into captivity shall go into captivity: he that killeth with the sword must be killed with the sword. Here is the patience and the faith of the saints.
The saints know that a better place awaits them after death than what they are going through on earth during the great tribulation.
So if the saints are not allowed to kill or wage war on the devil during the great tribulation while the devil wages war on them, what should be our mental disposition towards all enemies we meet in this life before the great tribulation? It seems to be generally, to love our enemies.