Georges St-Pierre's performance against Carlos Condit was endearing, and it earned him a unanimous decision victory.
That same performance against Anderson Silva would have earned him sublime unconsciousness.
This isn't to say that GSP is a bad fighter. He's the greatest welterweight of all time, but he's not Anderson Silva.
To see why Silva would triumph, look no further than St-Pierre's most recent performance against Carlos Condit as well as Anderson Silva's most recent performance against Chael Sonnen.
St-Pierre had a definite wrestling advantage against Condit. Thus, he managed to take Condit down repeatedly and keep him there. However, even with this advantage, there were still quite a few exchanges on the feet.
In one of these exchanges, Condit managed to land a head kick that floored the champ and nearly won him the fight.
If this momentary lapse in defense happened against Silva—a striker with greater size, accuracy and power than Condit—it would have been far more devastating. Even if the kick didn't finish St-Pierre, the follow-up strikes would have.
The counter-argument to Silva beating GSP is that GSP's wrestling would win out over Silva's striking. GSP would shoot his double-leg and smother Silva for the whole fight.
That's why it's important to look at Silva vs. Sonnen II.
Yes, Sonnen got Silva down in Round 1, but Sonnen is a far larger man than St-Pierre. Also, Silva managed to stuff Sonnen's takedowns in Round 2, ultimately winning in that same round by TKO.
Georges St-Pierre can't beat Anderson Silva.
Even if GSP manages to take the larger Silva down at times, Silva—being the greatest striker the UFC has known—will eventually land a hard shot. He's too accurate and skilled not to hit GSP.
If Carlos Condit, Matt Serra and Jake Shields can get at least one good hit on GSP, Silva should be able to get a dozen.
The beginning and middle of the fight might play out several different ways, but no matter how those exchanges end, Anderson Silva will always win one exchange: the last, giving the Brazilian the victory and solidifying his place as the greatest fighter of all time.