The word pastor means "shepherd". Jeremiah 3:15 says that God promises pastors after His own heart - pastors that will feed His flock with the right doctrine. The pastor is given the task to gather the sheep. 1 Timothy 3:1-7 says:
This is a true saying, if a man desire the office of a bishop, he desireth a good work. A bishop then must be blameless, the husband of one wife, vigilant, sober, of good behaviour, given to hospitality, apt to teach; not given to wine, no striker, not greedy of filthy lucre; but patient, not a brawler, not covetous; one that ruleth well his own house, having his children in subjection with all gravity; (For if a man know not how to rule his own house, how shall he take care of the church of God?), not a novice, lest being lifted up with pride he fall into the condemnation of the devil. Moreover he must have a good report of them which are without; lest he fall into reproach and the snare of the devil.
It's not enough that a pastor should be against sin but he should have a gentle side. As much as sinners need to be confronted but it's all about lovingly confronting them. It's possible to confront lost sinners without loving them but you can never love lost sinners without confronting them. It's a problem when certain pastors go overboard to the point they make lost sinners too angry to listen to the truth. It's just as misguided as pastors who water down the presentation of the Gospel just to get more people to attend their flocks.
The other side of the pastor is to drive away wolves. As much as they're called to be gentle but they must also learn to drive away wolves. This is all about confronting false prophets and not getting into fellowship with them. This requires the pastor to be stern about the truth of the Gospel. Romans 16:17-18 says:
Now I beseech you, brethren, mark them which cause divisions and offences contrary to the doctrine which ye have learned; and avoid them. For they that are such serve not our Lord Jesus Christ, but their own belly; and by good words and fair speeches deceive the hearts of the simple.
No false prophet or wolf in sheep's clothing will ever say they're lying. A good swindler will claim to always speak the truth and insist that his or her lie is the truth. Anybody can claim to always speak the truth and speak nothing but the truth even when they don't. The Pope always claims to speak the truth. Many executive ministers of pseudo-Christian organizations claim to always speak the truth. But the truth is Romans 3:4 says that nobody really always speaks the truth. Besides, Jesus already warned in Matthew 7:15-20:
Beware of false prophets, which come to you in sheep's clothing, but inwardly they are ravening wolves. Ye shall know them by their fruits. Do men gather grapes of thorns, or figs of thistles? Even so every good tree bringeth forth good fruit; but a corrupt tree bringeth forth evil fruit. A good tree cannot bring forth evil fruit, neither can a corrupt tree bring forth good fruit. Every tree that bringeth not forth good fruit is hewn down, and cast into the fire. Wherefore by their fruits ye shall know them.
Many false prophets are even known by their fruits such as habitual unforgiving behavior, a life of sinful indulgence, attitude problems towards everyone and how often they fail to show any concern for the redemption of lost sinners. While sin must be confronted but it must be done out of love. Any Christian should be watchful not just for pastors who teach Antinomianism or works salvation but also for pastors who think it's okay to massacre sinful people instead of evangelizing them.
Both voices are needed to balance the pastor. If a pastor is only gentle then he's catering to wolves. If a pastor is only all about driving away wolves but he ends up torturing the sheep in the process. To have one without the other is to be equally misguided.