Yep, we do have differing opinions on what bisexuality is. He recognizes there is a double standard and even admits to being obstinate in his stance on this topic. I can't change the way he feels - feelings are not right or wrong, they just exist. As a part of a couple, I foremost must respect his feelings and honor his wishes in this respect. He is softening his position a bit, which in my opinion is a move in the right direction - albeit a small step.
I am certain this will continue to be a source of discussion on and off and based on the replies to this thread, we have agreed to modify our approach. The preference itself will never change and I respect that boundary in our swinging activities. I can understand his point of view, despite whether or not I agree with it wholeheartedly.
We learn as we go, learn from experiences as well as from listening (reading) others' opinions. Heck, we've only been doing this 1.5 years and already we know so much more about ourselves and our desires than we did in the beginning. We work through bumps in the road together, sometimes agreeing to disagree. That's what marriage is all about - acceptance, compromise, and communication.