If the height of the heel is the same as the length of your foot, it starts to look wrong. And if the heel is positioned badly on the sole, you get into ballerina territory, where the body is pushed into a very strange posture. You can exaggerate the arch only so much.
What is sexual in a high heel is the arch of the foot, because it is exactly the position of a woman's foot when she orgasms... So putting your foot in a heel, you are putting yourself in a possibly orgasmic situation.