Yeah, this doesn't really support your argument. They weren't intentionally disrupting roleplaying events. They were playing the game in a way that is promoted and supported by Blizzard (you get an achievement for killing faction leaders after all). If you think a guild killing NPCs in Stormwind is "disrupting roleplaying events" then so is everyone running around on an obnoxious mount while roleplayers are nearby. You cannot sensibly draw the line here based on the feelings of some roleplayers. You're not making any sense at all.
Yeah, I do. Back in classic when it actually had benefits for your leveling. Nowadays you simply don't need to so it's a really dumb point.