GSP was always able to finish opponents. When he didn't have a title to defend, he generally finished as TS points out. However, the Tristar strategy was to play conservative, using an immense skill set that included a killer jab, TDD and takedowns to ensure wins.
People hate this because they want MMA to be like Mortal Kombat where every fight ends with a man floored in a pool of blood. And that's cool. I get that. I respect that. If that's your preference, fine.
But it doesn't mean that GSP didn't have the ability to finish. His gameplan was just to win with the lowest risk possible. Like most sports teams, he played to win and minimize risk.
And that is why he gets so much hate. Again, I get that that's a reason to hate him. But there's a reason why he's lost twice and Diaz has lost in double digits.