Then the question is how far does Magneto's honor code go? Why would he be disgusted with the Joker yet not when confronted with someone like Sabretooth? A poor comparison, granted, as Sabretooth has killed far fewer people than the Joker. However, a sociopath is a sociopath.
Personally, I think Magneto's whole "honor code" system is bunk. He's a mutant Hitler, when you get right down to it. Make whatever claims about "noble villain" you want, but Magneto shares many of Hitler's viewpoints and is in some ways worse. That's why I prefer villains like Darkseid and the Joker. They're bad guys with enough sense to realize it and revel in it.
Really, I'm looking forward to to how the Joker reacts and develops as a character in this merged universe. Maybe it's due to the whole Infinite Crisis deal going down in the comics, but I think it's going to be pretty cool when the Joker realizes there's a bad guy get together and he wasn't invited.
And to Master Bruce, cool! Will Lois and Jimmy be coming too? Or just Clark?