They think Cleese is going to take an angle on it that they don't agree with because he's an old man and the world today wouldn't let him get away with huge parts of what was in his work as a young man.
And because he's a brexiteer and that carries a lot of baggage.
but loads of people will watch - if only so they can tweet 'john cleese is a monster'/'john clesse is the ONLY MAN IN UK TALKIN SENS''