To me personally it's pretty simple - the more i like a girl, the more of her i want to taste and "eat" - this is where, for me, sucking and licking her feet come into play. It's kinda as you wanna "eat her inside out" or something: the "regular" (for the lack a better term) enjoyable parts of her body (tits, ass (thighs), pussy, mouth) are not enough and i want to enjoy more of her. I went once to visit an sp which i liked a lot by looking at her pictures. Once i got into the apartment, i've instantly concluded that i liked her even more in person - so i told her to get in doggy right away and started doing an intense DATO on her - just because i liked her so much and wanted more of her. Some other times, when i have an sp's legs on my shoulders, i start sucking on her toes as well - especially when i close to cuming. A couple of months ago a tried a black sp for the first time (i'm white) and liked so much the color contrast of our bodies and i sucked her toes hard. Another time, i was sucking an sp's feet and she started....laughing. I was thinking like wtf is funny about that, just lay back and enjoy. It didn't bother me or stopped me, but i always find it weird when women laugh during sex. Then she started telling me that she had recently went to the balcony without her slippers on - i was again in my mind wtf are you telling me that for. She was young and probably unexperienced. To conclude - for me foot fetishism is just normal and a part of "all other parts of the body fetishism".