I don't see the irony.
They assassinated him. They ended the discussion. There won't be any more good faith debates. The debates are over.
Now what?
Discussion
I think the irony is that he supported censorship and echo chambering while pretending to support free speech, even though he openly recognized that the consequences might include death
"Help, Lord, for the godly are no more; the faithful have vanished from among men" (Psalm 12:1)
Sorry, sardonic is the right word. It’s sardonic that someone would say that and then be killed for having debates with people.