I don't understand how retweeting makes one liable for libel. Isn't it just an attributed quote? Is accurately quoting someone really a punishable offense in the UK? This is a frightening idea, even outside the realm of Twitter.
Just an attributed quote? If I start quoting passages from Mein Kampf I'm sure my intentions are understood. But you're saying that I can just claim; "It's not me saying this, I'm just quoting Adolf, don't blame me".
People need to think before they act instead of just sheep herding themselves by mindlessly retweeting crap some other donkey is saying on the Internet. If a few of these idiots need to be taken to court as an example, so be it.
Taken to court for exercising their free speech rights? Even if it's "crap some other donkey is saying on the Internet", it's still protected by law in a lot of jurisdictions. And I'm thankful for that.
There is a difference between "free speech rights" and not taking responsibility for your free speech rights. Just because you have free speech doesn't mean you can (or should) be able to just quote anything or anyone without being accountable for it. If you feel like you should be able to retweet "crap" that's being said about someone without knowing the facts (defamation of character) you should also be man enough to be accountable if it turns out you were wrong.
Of course, it's good that a person be held accountable for their tweets and other communications. Neo-nazi or racist speech can be condemned, libel and false speech can be condemned. A person doing this can be outed as a bigot or liar.
But is that a reason for arresting a person? In the USA, the First Amendment to the Constitution says no. In other countries, apparently this is allowable, which is a dangerous tool in the hands of authorities.