To nourish affection for venial sin weakens the powers of our spirit, stands in the way of God's consolations, and opens the door to temptations.  St. Francis de Sales assures us that inadvertent venial sins and faults are "not a matter of any great moment" if as soon as they occur we reject them, and refuse to entertain any affection for them Francis make clear that the process of purification will continue throughout our life, and so "we must not be disturbed at our imperfections, since for us perfection consist in fighting against them."

Hatred for sin is important.  Confidence in the mercy of God is even more important.

May the Lord, who is good, grant pardon to everyone who has resolved to seek God, the Lord, the God of his fathers, though he be not clean as holiness requires. (2 Chron. 30:18b-19)