Quote Originally Posted by Angel Of Apocolypse
Seifer wasn't a bad guy, though. He is just misunderstood! He was trying to show Squall up and he was being manipulated and brain-washed. But I'm gonig to say, that I do feel sorry for him...cause I like him.
He was being manipulated, sure, but not brainwashed. The game tells us he was doing what he did of his own free will:

(The information given when using Scan on him during the fight with him in Deling City.)
Seifer
After leaving the Garden, he decided to become a Sorceress' Knight under Edea. Uses fire magic in conjunction with sword attacks.
(Bolded for emphasis.)

Seifer chose to do what he did. Ultimecia (in Edea's body) causing Rinoa to stand behind her against her will as she made her speech to the citizens of Deling City would fit the concept of being controlled, and her less-than-cognizant status during that time would suggest Seifer wasn't in the same condition even without considering what Scan says concerning him.