Credible allegations of pedophilia are exactly the sort of thing that defamation law should protect us from. Those are exactly the kind of lies that can destroy us as social beings. So I feel some sympathy for Cardinal Pell in taking legal action to clear his name when he (apparently) felt defamed by Catherine Deveny in a tweet that he evidently took as imputing pedophilia to him.
That said, I see most of Deveny's Twitter feed, and I doubt that there was any real imputation, let alone a credible one, that Pell is a pedophile.
No one suggests that Pell is a pedophile. What they do suggest is that the reputation of the Catholic Church for harbouring pedophiles is now at a level where a church hierarch needs to choose his words very carefully or they will remind his audience of pedophilia. When Pell appeared on the Australian TV show Q&A and used the expression "preparing boys", it immediately caused nervous-cum-malicious laughter from the audience, irrespective of the fact that he may have been trying to say "preparing boys for communion" - and that he added the extra words after the laughter began.
I watched that episode of Q&A. I have seen a lot of Twitter discussion of it. None of that discussion seemed, to me, to suggest that Pell is himself is a pedophile. I am very sceptical that Deveny's impugned tweet did so (it has now been taken down, so we can't easily check for ourselves). But the extensive Twitter discussion does suggest some public concern over the amount of pedophilia in the church, and over the church's responses to it - responses that have involved blame shifting, atrocious priorities, and much all-round managerial incompetence. If the church and its hierarchs are now associated in the public mind with pedophilia, that is the fault of the church's worldwide hierarchy. Yes, the discomfort and censure is mixed with a certain amount of malicious glee ... but the church, through the cumulative actions and statements of many of its leaders, brought all this on itself.
Since I'm not sure that I've seen the actual tweet that is impugned, I can't be sure that it contained no outright imputation of pedophilia. Therefore, I can't be sure that the defamation action by Pell is unjustified. However, I'm very sceptical. I think it's right to be sceptical when we see this kind of legal action taken by a public figure. To be fair, Deveny is also a public figure, and anything she says in public will be heard or read by many people. There is not a total imbalance of public reach here. Still, I'm sceptical. In fact, I'm always sceptical when I see a powerful person reaching for the defamation button.
I'm also sceptical when I see threats to sue Twitter itself. I can see the point of being able to demand the details from Twitter of who owns an account - subject to judicial oversight - but a social medium like Twitter should not be legally responsible for what is said by the individuals who use it, any more than my phone company should be legally responsible if I defame somebody during a telephone conversation.