It's a non-optional social convention.

‘That all you wish to do is rescue these poor slum-dwellers, Balfour, we quite understand. But it is not always so easy to separate a contempt for the streets on which a man was born from a contempt for the man himself. You have heard that silly Christian expression: “Love the sinner, hate the sin.” But Jews know that a sin is not something that you can cut out of a man like a polyp. And nor is the memory of his home, filthy as it may be.’ Berg paused. ‘You do not hate Seth, but wish he had not grown up in a slum. There are other reformers like you, I dare say, who do not hate Seth, but wish he were taller and had all ten toes. And there are still others who do not hate Seth, but wish he were not a Jew.’
‘I don’t quite understand what you’re trying to imply, Rabbi,’ said Pearl. ‘I merely wish the best for the boy, and for all boys like him.’
‘In the world you seek, there would be no boys like him.’