Continuity mistake: During the prison fight scene, Silk Spectre's stiletto boot heels are alternatively flat-soled from shot to shot, for the stunt woman's benefit.
Revealing mistake: During the final confrontation in Veidt's lair, you see the actor Billy Crudup in his SFX suit reflected in Nite Owl's goggles, not the image of Dr. Manhattan.
Trivia: This is for the trailer rather than for the final film, but worth a look. At 1:33 in the trailer, just after seeing Rorschach slam someone against a wall, we see another fight. Pause it and look at the guy in black - he's holding a walkie-talkie, which in the next shot becomes a gun. This is only trivia, not a mistake, because it's only valid for the trailer. The MPAA don't allow guns to be pointed at the screen in trailers, so Zack Snyder, in a tribute to the infamous gun-editing from E.T., replaced the gun in that one shot with a walkie-talkie. (00:01:30)
Other mistake: During the Comedian's funeral, in a shot from above showing both grave and the casket, the grave is actually shorter than the casket. (00:33:55)
Revealing mistake: When Veidt and his cat Bubastis is walking over the bodies of the scientists after he poisons them, you only see Veidt's reflection and not Bubastis' in the energy panels on the walls as he walks towards and up the stairs.
Visible crew/equipment: At the beginning of the movie when the Comedian is fighting with the mysterious masked man in his apartment and the first one is launched towards the table, the director Zack Snyder is hidden behind the kitchen counter and kneeling (this mistake is revealed by Snyder himself in the DVD extras).
Continuity mistake: When Dan returns home after talking to Mason, he finds Rorschach in his kitchen eating beans from a can. After he has finished eating, he throws the second can on the table where it lands next to another can. When he gets up, the two cans have moved significantly apart. (00:20:15)
Answer: He has spent years as a costumed vigilante despite the fact that it was illegal. He has a very strict idea of what is right ("never compromise") and has proven himself incapable of doing otherwise. So no, there was no real chance of negotiating with him - Rorschach himself made it clear he'd have to die if they wanted his silence.
Garlonuss ★
Death was not the only choice. Doc M could easily have teleported/banished Rorschach to Mars/anywhere secluded in an oxygen bubble. He could have spared his life and just made him mute or manipulate his brain chemistry/atoms to remove the memory of what happened. The point is Doc M is all powerful and could manipulate matter at his whim; death was just a plot device creating a chance of an emotive martyrdom/sacrificial ending.
Ethically speaking, exiling him to Mars or erasing his memory of the event can be considered just as cruel as killing him, because then his agency is being taken away from him. Rorshach's malcontent with the situation poses a problem for the other heroes, and since Dr. Manhattan isn't willing to let him tell the truth of what happened, he obliges Rorschach's demand that he kill him instead.
Phaneron ★