Remember in Season One when Loras had a find political acumen and could be a skilled manipulator?
Renly's death has essentially killed Loras' brains, I'm convinced. Because there's no way in hell Loras would've fallen for Oliver's tricks were this Season One.
But then again, my lovely Lady Olenna has foretold of this dumbing down of Loras... because all he's good for is hitting men off horses with a big stick, am I right?