Regarding the For XY Discussion Only!! forum concerning Caius and his attitude.
My belief is it took several instances/incidents for how he became that way.
One of the Children of the Moon almost won against him, Extra Abilitys could have prevented that. Frustration at his lack of Abilitys then, made him sullen and forming his wish to enforce rules vigorously against them.
Other Volturi could both use their powers and be feared because of those powers, further fueling his attitude.
Not being able to use any Extra Abilitys when at court, he could have approached that with extensive searching of how to use the laws against people. Even bending the laws best as he could to force judgment on someone. Releasing his anger and providing a fear of him, as a part of the trio.
Aro, having seen his devout outlook on Laws and attitude would use that to his advantage. Becoming a lawyer of the trio, seeking out any flaws in their defence. Enforcing his belief that his way of approaching laws and attitude is the right way for him.
This is just my outlook on him, and was in response from the For XY discussion Only!! thread about Caius
Well that wasn't exactly the reaction I'd been going for, 123 p. of SM's Partial Draft.