This is a popular slogan at the moment. How should a Christian respond?
Well, given how foundational love is to the gospel—how much of a ground-level concept it is to Christianity itself—I think every Christian ought to spend serious time thinking through the doctrine of love. What is love? That’s something we should all have an answer for.
But more briefly, let’s take love as very broadly referring to a relational force that holds us together. In a secular world, that’s just a matter of emotion; and without something deeper to ground it, it’s ultimately meaningless, regardless of how good it makes you feel at the time.
But for a Christian, love does have a ground. It is grounded in the Trinity. That’s where love originates; that’s the exemplar for love. The problem is—at least, it’s a problem for “progressive” Christians—this means it is not an indiscriminate relational force. It is a relational force that ultimately finds its fulfillment in God.
But since God is holy and good, it is a relational force that ultimately excludes any sin.
So when someone is engaged in gross immorality, loving them does not mean just supporting them or approving them no matter what; it must actually mean correcting them and helping them. Indeed, this is the only way we can relate to them that actually is love. This is because, if love ultimately ends in God, but “neither the sexually immoral, nor idolaters, nor adulterers, nor men who practice homosexuality [etc] will inherit the kingdom of God” (1 Cor 6:9-10), then to pretend that homosexuality is normal and good is actually to hate someone. It is to exclude them from ultimately fulfilling that relational force in God. When you act in a way that ends up excluding someone from heaven, you are acting in a way that will finally deny them love forever.
Love is not a temporary, comfortable relationship with someone here on earth, where you ignore their sin to get along with them and have a good time. Love is an eternal, unbreakable relationship with God and his people in the world to come. Sacrificing the latter for the sake of the former, rather than sacrificing the former for the sake of the latter, is ultimately to hate them.