Is it okay for friends to kiss?

I was thinking about this in the shower the other day, and found it interesting how there are different levels to gestures. A hand shake, a hug, a kiss on the cheek, then the lips, and ultimately close contact that leads to sex. Why do these gestures exist? Maybe Its how we express care, sympathy, acknowledgment of another person and communicating to them the level of relationship you share with them. It got me thinking, If these gestures are how we express care for another person, why is a kiss, or even worse, sex with a friend seen as a bad thing? I know the purpose of sex is to procreate, but it also is one of the most intimate acts two humans can have with one another and ultimately it shows something. It shows the ultimate level of attention, care, dedication to another person. I mean, that's why when someone cheats its seen as a disloyal act. You can't have two favorites, one will always be lesser. How will the lesser feel knowing the other has the majority of attention/care/dedication? To me, this is why in a committed relationship cheating just shows lack of care to stay committed to a partner, and ultimately makes one feel abondoned because there is no other gesture that expresses attention/care/dedication more than sex.

Back to the kissing topic, I think since all these acts are a form of expressing different levels of care, why not express your care for a friend in the form of a kiss? it does not share the same level as the gesture of sex, and If its done with the intention of showing that you care for someone wouldn't that be a good thing? Would it ruin a friendship? is it ok to have a friend that is that close/ expresses that level of care with another friend? is it only okay if the two people are single?

Thanks in advance!
Is it okay for friends to kiss?
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