I don’t think Jesus ever said, “We must hate the sin but not the sinner.” On occasion, He actually spoke quite harshly about sinners “Woe to ye scribes and Pharisees . . . “ etc. Maybe the quote comes from somewhere in the Old Testament, or maybe it’s of more recent origin.
Jesus died so everyone could be saved. If that’s not love then nothing is. 2 Peter 3:9 says that the Lord is “longsuffering toward us, not willing that any should perish but that all should come to repentance”. But since we all have free will, not all will come to repentance. In order to be just, God will punish those who won’t. Rom. 11:22: “Therefore consider the goodness and severity of God”. Sodom and Gomorrah experienced His severity. Speaking harshly to and about sinners is necessary for their own good and that of others. Harshness does not necessarily mean hate. Hate is a self-consuming dead end street. I know from personal experience. It nearly ruined my life.
Reading comprehension involves the act of deriving ideas present in ways other than those that are simply and explicitly stated in a concrete sentence. In fact, ideas presented in such a way are often more relevant and powerful than something taken directly from a verse.