Only if it advocates violence or is likely to incite violence should a book be censored. I have read some of the thankfully late and completely unlamented
Colin Jordan's scribblings online, including a novella he wrote about a violent fascist revolution in the UK. It was appalling, and I don't just mean literarily, though certainly that. I think it is banned in print form in the UK, but it's near-impossible to ban things from the internet. It certainly should be banned, as it not only fomented hatred towards Jews, blacks, and liberals, it provided useful information for would-be terrorists. I wouldn't want to ban 'The Merchant of Venice', 'Oliver Twist', or some of Doyle's Sherlock Holmes stories, all of which can be accused of anti-semitism, and some of the ACD stories of anti-black prejudice, nor do I think any modern equivalents should be banned, provided they don't advocate violence.