GSP has nothing to gain by doing this fight... and so much to lose. Right now he's considered one of the best fighters there is... and he can retire as one of the all time greats. Not only does he have his legacy... but he has a whole bunch of endorsement and business deals which rely upon him being "the best". He could lose a lot of that with one swift KO front kick to the face.
More than likely if they fought... Silva would just destroy him in a manner similar to how he usually finishes his fights... and GSP instead of being one of the all time greats will be remembered as that "guy" who got KO'd in some creative and crazy way.
GSP has too much to loose in taking this fight.
What? He has all to gain and nothing to lose because he's challenging Silva at his weight. The person who would lose alot is Silva.
Silva winning would fill this forums with "Well he is bigger than GSP", "Size advantage blah blah".
But with Silva losing, you'll see this: "Silva was overated!", "GSP THE BEST EVARR RAWRRRRRRR HE BEAT SOMEONE BIGGER THAN HIM RAWRRRRR"
I done wrestled with an alligator, I done tussled with a whale;
handcuffed lightning, thrown thunder in jail;
only last week, I murdered a rock, injured a stone, hospitalized a brick;
I'm so mean I make medicine sick."
- Muhammad Ali, 1974.