I think it's only fair to say that it's not HIS assassination of Lex. I mean, someone wrote that shit for him to say, someone green lit that persona as well, as they thought it was working for the mood of the film. It's highly likely that Jessie didn't even like the portrayal, and maybe even spoke up about ways to change it, but was shot down, because he's just an actor. I vaguely recall hearing mention about Ben getting frustrated with the production, as he, a director/writer in his own right with considerable talent, apparently tried to do some tweaks with the story, etc, but was shot down. So, it's entirely possible Jessie was just, doing a job, as he was contractually obligated to do. With little to no input on how he was to portray the character. Which happens a lot more in the acting world than I think we realize.
In the fan-spheres, we often describe characters as if they are the brain child of the actor themselves, when it's more often the character is already fleshed out, and the actor is just, well...ACTING like the script instructs.