Of course, a woman's foot is literally the lowest part of her body. Kissing her foot can be humiliating, which is part of the thrill. Since ancient times, the kissing of the foot has been a sign of submission. The foot slave is happy to humble himself like that, to kiss her foot, even the bottom of her shoe, while groveling before her, lying prostrate on the ground, as low as he can go. If he does a good job, she could reward him by massaging his throbbing member with her foot, or placing it between her heel and backless slipper.
Some foot slaves exhibit a reverent devotion to the feet of their mistress, their goddess.
Their worship is only partly sexual. They feel that since most women are not as violent as most men, males need to feel the controlling influence of a female foot on them every so often. The feminist male foot slave surrenders himself to the civilizing, sexual power of Woman via his mistress' foot or boot, going beyond roleplay into serious sexual politics. But feet are fun. Feet are innocent.