Correct me if I am wrong, but ignorance is not a defence in the eyes of the law and certainly not in any potential civil suit if he were to seek damages for defamation.
Under law we all have certain obligations where ignorance is not an excuse, but generally it's exhibit A, B and C in many legal matters. As far as I'm aware, I thought it's considered as mitigating circumstances or adds context, but as an excuse on its own it carries no water or merit. While ignorance can be no excuse for certain things, in the details it becomes an incredibly useful tool to absolve of culpability.
I think here, you're looking into what is reasonable ignorance, it's surely a wise idea to establish and punish more significantly if comments are malicious, rather than naive. But defence team then has case to demonstrate the levels of ignorance of defendant, especially on the more prominent matters. Generally anything that harms your defence is generally a good thing to forget about prejudgement.
Law takes people's situation and position into account when making judgements, a man under duress may act out of character. But also the accused sometimes literally had no knowledge what they were doing was illegal and I'm sure there are many examples of things that are illegal, but you may not consider immoral.
Do a peaceful protest at a nuclear facility, do a comedy routine about terrorism in a sensitive area and you may be punished in a way that seems disproportionately harsh. But morality and legality don't always meet, defame a small business owner and you'll probably be refused service, defame a powerful, rich business owner and you'll find your life on hold for years while they fight you in court case after court case.
My general rule is that it's not worth picking battles with people prepared to go to war, and you need to be wise before choosing to do so. McKenzie is exactly the sort of person who fights all his court cases in the public domain, as that's where most of the judgements are at least framed. But he tiptoes in to the most offensive territory, because he is reassured about the law and what is permissible in court.