I don't see why bisexuality has to be commented on and criticized so much. At the end of the day, sexuality is a spectrum, and everyone fits in different places on that spectrum. Imagine that every human being has a percentage value, where 100% means they're totally heterosexual, and 0% means they're totally homosexual. Then on such a scale, I would place myself at around 80-90%. I'm certainly not gay, but neither am I completely straight. However, I certainly don't consider myself bisexual, despite the fact that I'd be willing to have sex with a man even though my overall preference is for women. I don't see why there has to be such a big fuss about it.
Here's another example, too, regarding the original idea in this thread, that bisexual people are 'greedy' for liking more than one gender. I have an ongoing fictional universe ready to start writing a series about, based around several students. Now, one character, a girl, falls in love with a guy, but he's seeing someone else, so she doesn't do anything. Later, she meets another character who is openly lesbian. The two become friends, and gradually become really close. The girl happens to have long had a physical attraction to other girls, but she still loves this one guy, so over time realises and comes to terms with the fact that she's 'bisexual'. Her lesbian friend helps her come to terms with that, and the two start a relationship. The relationship ends later when the first girl decides to split up with the lesbian girl, to pursue a relationship with the (now single) guy she was originally in love with. Bear in mind that she does love the lesbian girl as well, just not as much as she loves the guy, and has always loved him anyway.
In that scenario, is the bisexual girl greedy? Or is she simply following her own heart and making a valid decision based on her feelings? Any comments would be welcome, because this is a prime example of what people don't understand about so-called 'bisexual' people. It's not a matter of being greedy about who you like to have sex with. If you're truly bisexual then you have feelings of love and attraction to both genders, that's all there is to it. I just don't see what's so 'greedy' about that.