I suppose it should not surprise me when folks who promote a false grace—making it a license to sin (see Tit. 2:11-14; Jude 4), and a false faith—that is void of works of obedience (see Rom. 1:5; 16:26; Jas. 2:14), also practice a fake love.
According to the New Testament, the primary mark of one who is truly born again is his love for others who are born again:
We know that we have passed out of death into life, because we love the brethren. He who does not love abides in death. Everyone who hates his brother is a murderer; and you know that no murderer has eternal life abiding in him (1 John 3:14-15).
John stresses both the positive and negative. Love identifies the genuinely born-again person. Lack of love, or even hatred, for those who are born again identifies the false Christian. As difficult as it may be to accept, people who promote a false gospel that advocates a false grace and false faith are not genuine believers in the Lord Jesus Christ, which explains why they are often so nasty towards those who are genuine believers. They will slander you behind your back, even as they sometimes pretend to be your friends to your face.