As for my actual opinion, I don't see any problem with contacting the GM so see what happened with the situation, but otherwise I agree with Robin and Lisa.

To the OP and the detractors in this thread, the point the article is making isn't saying you should condone ninjas or give them second chances. It's saying you shouldn't escalate drama just for the sake of your own moral justification. While some people may feel validated in doing so, especially if there really is foul play abound, purposely creating drama makes you appear to lack dignity and respect no matter how justified you are. If your actions create conflict that hurts innocent people and your justification is 'I'm doing what's right,' that's not justice, that's being vindictive. And most of all, it makes you look like a dick.

If the guild is really that bad, then leave. If it really is run by a corrupt GM and lets ninjas get away without punishment, it will gain a reputation for such or simply collapse from the corruption. THEN you can go back to whomever remains, say 'I was right' and get your moral validation.