from my point of view…

It’s fairly interesting, because in the novelisation, Mace does call him on it:

Victory flooded through Mace’s aching body.  He lifted his blade.  “You Sith disease-”

Wait-” Skywalker seized his lightsaber arm with desperate strength.  “Don’t kill him-you can’t just kill him, Master-”

“Yes I can,” Mace said, grim and certain.  “I have to.”

“You came to arrest him.  He has to stand trial-”

“A trial would be a joke.  He controls the courts.  He controls the Senate-”

“So are you going to kill all them too?  Like he said you would?”

Mace yanked his arm free.  “He’s too dangerous to be left alive.  If you could have taken Dooku alive, would you have?”

Skywalker’s face swept itself clean of emotion.  “That was different-”

Mace turned towards the cringing, beaten Sith Lord.  “You can explain the difference after he’s dead.”

I prefer the book to the film in many places.  Lots of detail and description, and even some thing that were cut from the movie, like the Petition of the Two Thousand.