I tend not to think I know better than the writers. I will say one thing, though.
To me, Xorn was Magneto and Magneto was Xorn. He did send New Yorkers to their deaths in gas chambers. Wolverine killed him and the only reason he was able to return in Excalibur and later in Avengers Disassembled was that his daughter wanted it that way.
There is nothing about Magneto's character that says to me, especially while he was high on Kick, he wouldn't have killed those New Yorkers.