Wow. Just because I called you on using the topic as a facet for you to assert your 'beliefs' (and yes, I do, for most of what you say, mean beliefs) doesn't mean you need to analyze every detail and break it down in hopes to make yourself, simply put, look justified.
First of all, words are made by people, and therefore defined by people. Feet may not be a nonsexual part of the body in terms of directly, but guess what? Technically there's only one bodypart that would be truly 'sexual' in such a way. The butt and breasts, however, are not necessary for actual sex in it's purest form. They are, rather, the bodyparts which, over however many years humanity has been growing, have grown to be seen as such due to a long-time attraction to such places by the human species. It's just how things evolved. If such a thing had happened to feet, it could easily be considered 'sexual' as well.
Second, tell me, what exactly makes feet and tickling go together better than bellies and tickling, or hips and tickling, or any bodypart and tickling? If it turns you on, fine, but claiming one commonly ticklish bodypart goes better with tickling than another is simply an opinion, and ONLY an opinion. It's an opinion because it is YOUR belief, based on you being into it. This doesn't make someone with an armpit fetish 'less correct' than it does you for associated tickling with it.
And yes btw, people DO choose for them to be considered 'together', unless one has a specific fetish for ticklish feet I suppose. While it is true that such tastes can be imprinted on one's genetics, it is not always the case. Many people's tastes grows based on childhood experiences and influences. Go around and ask how many here prefer feet to tickling. Then ask if the only reason some here are into tickling is because of feet. Then asks if they have any experiences in their youth that exposed them highly to feet. The individual often choose to associate the two due to one being a facet for the other. While there are obviously many different cases, more often than not people don't associate the two so strongly because it's in their genes.
Of course, I expect you'll respond with a huge rant on how I'm wrong while trying desperately to prove it, even though it'll probably end up making you look YOU used this thread as an outlet for what you believe (and hope, in the 'more foot people than you realize' thing), but I don't much care since I've already stated my thoughts on the matter.