The worst sin is assigning partners to God and He's made it clear that it's the only sin that He will not forgive if you die in a state of polytheism.
As for "Thou shall not kill." contrary to popular belief, that doesn't mean that someone defending themselves and killing their attacker, or someone that decided to start killing the neighborhood child molestors and drug dealers would be breaking that Commandment. Someone like George W. Bush, Jim Jones (the real one), David Koresh and others are definitely in violation of that Commandment and will answer for it.
Don't forget that in The Gospel is says, "An Eye for an Eye and a Tooth for a Tooth" and in The Qur'an it says, "Take not the life that Allah has made sacred, UNLESS by means of equal retaliation, OR if that person is causing mischief in the earth."
This "George" that Ms. J. was talkin' to is a moron in reality, because all this, "Vanity" crap just proves that he has no clue at all what he's talking about. If you're attacked, you have to defend yourself. It's our nature. Hell, look at the lower animals. When you see a lion that's just caught it's prey, and there's Heyenas in the backround and one of them gets the nerve to try and step to the lion, usually the lion will roar, bear it's teeth and swipe at the heyena, as if to say, "Don't f**k with me, because I WILL kill you."
There's really no difference between them and us. It all comes down to defence of territory. Maybe if people weren't such pussies these days, it would be more evident.
Also, that crack about, "There really is no truth because it all depends on what you believe..." Wtf?? So, whatever we assume is automatically true simply because we thought of it?? He's a moron I tell you.
If you make your enemy react, you've won.