If a man say, I love God, and hateth his brother, he is a liar: for he that loveth not his brother whom he hath seen, how can he love God whom he hath not seen? And this commandment have we from him, That he who loveth God love his brother also. (1 John 4:20-21 KJV)
It's simple logic. A Christian is supposed to love others as God loves him. However if a person hates others, then it's obvious that He does not know God or love God because if He did he would show love for his fellow man.
Once again it should be pointed out that it is not unloving to show people what the Bible says about sin and judgement.
There are those who would say we should be accepting and tolerant of sinful lifestyles. With a view to the judgement day, this would be like standing by and not saying anything to the person sleeping in a house that is on fire. However, our presentation needs to be tempered with compassion. Standing on the street corner holding signs that are name calling, telling people God hates them and they are going to Hell while laughing and joking around with your friends isn't showing Godly love for anyone. That is a major turn off for anyone that might be interested in the things of God. Clearly, that is not love.