So, let's say you're an Olympic athelete and you feel the need to share your disgust with the whole China-Tibet thing so you show the Tibetan flag.  What do you think China will do?  Since they are such an advanced country capable of withstanding criticism, they will expell you, which is better than being thrown into one of their prisons to be sure.  And, yes, that was sarcasm, for those of you who are sarcasm impaired.

"competitors were free to express their political views but faced sanctions if they indulged in propaganda."

Er.  Yeah.

Athletes who take Tibet stand 'face Olympic cut'

Honestly, why would anyone in their right mind hold the Olympics in China anyway? Olympic Flame Now 'Symbolizes Repressive Regime'