A nation that abhors boycotts should not cast the first ban. Israel has made some bad cultural moves down the years but none is potentially as damaging as the pointless decision to deny entry to Gunter Grass.

Grass is one of the few epochal writers alive, a novelist who changed his people's perception of itself and helped the world to achieve a deeper understanding of the horrors of the 20th century. From The Tin Drum (1959), which presents a boy's-eye view of the Nazi period, to Crabwalk (2002), bridging end-of-war to fall-of-Wall, Grass has consistently challenged the political narrative by presenting massive events from an individual perspective. He is, by any definition, an important writer.

Last week, at the age of 84, he published a poem that criticised the state of Israel and German policy towards it.

When a great novelist turns to verse, it is usually a sign of failing powers and the world kindly turns a blind eye, as it did with the late rants of Harold Pinter. Grass, though, is too big to ignore. German newspapers denounced his poem as antisemitic, reminding their readers that Grass - like the Pope - was once a teenage soldier in the Waffen-SS.

Grass went on TV to defend himself, arguing that his poem was an attack on the Netanyahu government rather than on Israel. That government, through interior minister Eli Yishai, then banned him from the Holy Land.

The decision undermines Israel's free-speech principles as well as the freedom of its artists to carry their message abroad. Pro-Pal writers and artists will soon boycott Israel "in solidarity with Grass". Those who defend the Israel Philharmonic and Habima in London have been lamed by the Grass ban. Netanyahu and Yishai have just accelerated Israel's cultural isolation - and for no good reason.