Lines can be dotted, blurred, red, green, drawn, shifted and crossed. To “cross the line” means to stray into the unacceptable, which may be defined by law. This week, Jews were asking where the line was when it comes to inciting hatred on social media.

It follows a Google executive’s staggering explanation to MPs on Tuesday as to why his company – which owns video-sharing website YouTube – had not removed a video featuring white supremacist David Duke. In it, Duke accuses Jews of encouraging “white genocide” by bombing babies in their sleep and massacring thousands outside Israel’s borders to foment hatred between non-Jews. None of this “crossed the line”, said the executive, despite video viewers commenting that Jews should all be hanged.

In the UK, the Racial and Religious Hatred Act 2006 makes it a criminal offence to incite hatred against a person on the grounds of their religion. Several laws before this made it an offence to deliberately provoke hatred of a religious group, distribute racist material to the public, make inflammatory public speeches and incite inflammatory rumours about an individual or an ethnic group, for the purpose of spreading racial discontent. If that’s not what Duke’s doing, we don’t know what is.

Duke’s broadcasts reach Britain, but are made from America, where the First Amendment protects freedom of speech. And herein lies the problem. Laws differ in different jurisdictions. In Germany, where Holocaust denial is illegal, Facebook last year hesitated to remove a neo-Nazi group’s feature titled ‘Jews among us’.

Posted on the anniversary of Kristallnacht, it included a map showing the locations of 70 synagogues, care centres, organisations and businesses. Facebook at first said it fell within its free speech guidelines, only to remove the post later following a social media outcry.

The situation is untenable. Hate kills, yet it is spread with increasing ease online. We’re not talking about reasoned arguments against Israeli policy here. We’re talking about out-and-out Jew hate. Of course it “crosses the line”. It’s only home is offline.