Chelsea say they sold William Gallas because he threatened to score an own goal if he was selected for their first game of the season. (http://news.bbc.co.uk/sport1/hi/football/teams/c/chelsea/5314292.stm)

This was because he wanted either a pay increase or a transfer. He denies the allegations but I don't know if any defamation law suit will follow.

Now I've heard of similar stories before. Tony Cascarino wrote a piece in The Times stating that he'd played in teams where a player wanting a transfer would make a nuisance of himself to get it. This would include giving opposition teams information on line ups, tactics, set pieces.

Is everyone united in condeming this type of action or is a player entitled to do whatever he can to secure a release from his contract if his club won't allow him? Have you heard of similar stories?

I have not heard of similar stories. In fact I am not 100% convinced that Gallas did what Chelsea accuse. But I certainly condemn such action if it has taken place.

At the end of the day a player signs a work contract for a given period of time. They can negotiate, or even terminate the contract if all parties agree, but if not they are bound to the contract. Actions of underperforming, giving away team tactics/formations are not what a club would expect from a professional employee.

Could be a good time to play against Bayern ...

Hmm. Childish behaviour, which real people wouldn't be allowed to get away with (presuming it's true...). Essien's refusal to play any more for Lyon when Chelsea came knocking, regardless of the contract he had previously signed, was on the same sort of pathetic level IMHO.

Could be a good time to play against Bayern ...
Indeed. Hargreaves current behaviour is just one example of this.

And of course this behaviour should be condemned and the player in question be insulted in every possible way whenever he returns as an opponent.