It's because a lot of people, gay and straight, define themselves and the world around them so much by orientation that the concept of fluid sexuality frightens them. They can cope with someone doing both sexes as long as they can convince themselves that the person is "confused", and that they'll resolve themselves eventually to the ideal - one sex or the other.
You can never read too much into anything! Imagine if Dan Brown had just been like "meh, whatever". Nah, what I was saying was that you're one of the good ones who doesn't feel the need to off-load their own hangups onto others. It's a good thing.
Amen. I find myself sexually and emotionally attracted to members of both sexes, so I appear to fall within the bisexual category. Ah well. Whatever people want to call it is fine by me. I've just got a heart filled with loving.