I have been accepted to an event where a keynote lecturer is a plagiarist After some decades an event on my research area was announced in my city, so I decided to send my abstract, which was accepted.

However, they recently sent me the programme and among the keynote speakers was a person whose doctoral thesis contains uncontroversial plagiarism. (About 30 pages of his thesis are just a translation from two papers written in English by other scholars into the language in which the thesis was written.) There are no legal charges against this lecturer. Instead, the plagiarism was revealed by an apparently anonymous source about two or three years ago through a mailing list.

I know that at least some of the organisers of the event were in such mailing list, so they do not ignore the charges and had the chance to test whether they were true or not.

I have considered that maybe the best option to withdraw my lecture from the event explaining exactly why to the organisers. This, though, would not help at all, since they already know and do not care. Else they wouldn't have invited him as keynote speaker.

Other option that somebody suggested me is that I use some minutes of my lecture to publicly denounce him. (It just happens that my regular lecture starts right after his keynote lecture finishes.) But there are three problems with this:


When publicly denounced, this lecturer threatened to prosecute the source for defamation. (He's also lawyer.) I currently do not have a job nor a regular income that would allow me to face a prosecution, let alone to prosecute him.
It is very likely that most of the people that are going to the event already know. In such case, and since this is fairly yesterday news, I do not expect that there be any important reaction.
I am about to enter in the phase of defending my thesis, and this lecturer works in my institution as invited professor. Unscrupulous as he is, he may try to retaliate against me by using his power to delay my thesis dissertation. (I do not know how much power he has.)


Finally, you may be surprised as to how a whole academic community could care so little about this case. But I have to say that when the news about his plagiarism came, I myself didn't dare to publicly speak disapproving his behaviour because of what I said in the third point. Still, it was surprising to me that, although I know that several professors disapproved of his actions, apparently none of them publicly manifested their disapproval. I later knew that this wasn't the first time that something like this happens in my institution.

I'd like to know what is the most ethical or less unethical thing to do in this case. One thing is for sure, though. I do not think it would be right for me to go to that event, and speak after him as if he were a respectful scholar. And I am not going to.

Thanks in advance for any advice.
What really matters here is what your goal is. Is your goal to: (A) cause there to be some sort of disciplinary action/reaction against this person; or (B) to make sure that your own name is not tarnished by association with this person in the future. 

If you are hoping for (A) I believe that you have answered your own question. It does not appear that any action will be taken against this person based on anything you do in relation to this conference. The discipline is covering this up and everyone is going along with it and as an early career researcher, you are not influential enough to change this. It's sad, but it's true. However (B) is entirely possible for you. If you believe that one day this person will be publicly shamed and denounced fully by the discipline, it is not unreasonable for you to not want your name associated with theirs. This might mean withdrawing from the conference and specifically asking that your name be removed from any material online about the event. Indeed, you don't even need to say why you are pulling out of the event if that includes a risk that it will get back to the person in question. 

In this situation, I think (B) is a reasonable concern and a reasonable reason to not speak at a conference. I also think that you are tangentially associated with this person so are unlikely to experience any negatives from speaking after them at the event. Ultimately, with risk of association low, it comes down to your own ethical stance and if you feel sharing a stage with this person violates that.