I think a seperate axis for each gender would be better than the single line scale, but, either way, I think the scale is a useful model if you factor in that a persons sexuality is not a fixed point on the scale, but can move about depending upon circumstance.
That's just it. I don't think it's simple depends on circumstance. It's a mixture.
Look, I compare what gets a person aroused is like what kind of food a person likes. For example, I hate tomatoes. Can't stand the taste by itself. I pick them off a sandwich if someone puts sliced tomatoes on a sandwich.
But - crush them and make them into a sauce and put them on a pizza or pasta. Okay, I like it that way. So even though I like tomatoes as part of a sauce, I can't stand them alone.
The basic desire is attraction to tomatoes isn't there, but in a certain circumstance, yes.
On the flip side, peanut butter is the world's most perfect food. I love peanut butter more than any other food I can think of -- except on bananas. Or tomatoes. Or mixed with honey (bleh). Or.... you get the point.
The basic attraction to peanut butter is strong, but given certain circumstances - no way!
Why do I hate tomatoes? I don't know. Just do. Why do I love peanut butter so much? I don't know. Just do. Now since I like tomatoes a certain way in a certain situation, should we put it on a scale? How do you scale taste?
I feel the same goes for sexual attraction. For example, I am heterosexual and I couldn't take my eyes off Olivia Wilde in the new Tron movie. In fact, the first time I saw it, all I could see was her. Then I saw her without the Tron get up and I thought "Meh. She's okay." Where does that put me on the "scale"?
ETA: Actually, I thought of a better example. Take Olivia Wilde in the Tron get up, being Dominate over a man or a woman, and forget it. I wouldn't be interested in the least bit. In fact, that turns me right off. However, put her in a situation where she is submissive to a man and HELL YEAH! ...how do you scale that?
There can be no scale to it. There is a basic sexual attraction (or taste) that one cannot change, just like one likes peanut butter but hates tomatoes. But in a certain situations, other factors, such as emotions, social pressure, intelligent reason, hell even intoxication, etc, etc, can make one enjoy tomatoes and hate peanut butter, but the basic attraction does not change.
IMHO, this is way too complicated to simplify basic desires, fantasies, tastes, emotions, thinking processes, hang-ups, reasons, inhibitions, etc, etc into a scale.