“If anyone has no love for the Lord, let him be accursed.”
That’s a very strong statement. Catholics would say, “Let him be anathema”, which simply means “devoted to destruction”. Paul leaves us no fence to straddle: it’s love or destruction. Choose one or the other.
That word translated from Greek to English as “love” refers to affection or approval. It’s also a word that means “to kiss”. In the ancient East, when you saw someone you knew and liked on the street, you would greet them with a kiss. It was a way of publicly identifying yourself with that person; of saying to everyone around, “This is my guy, right here.”
Or you could just turn your head away and walk on by. But what an insult that would be.