Saliva or Spit?

The other day in class, our teacher casually asked for a volunteer. The kid who was chosen didn't know what he got in to. Our teacher handed him a spoon and told him to spit in it. The class cringed wandering how spitting in a spoon related to sociology in anyway. The student did as he was told. The teacher talked of how saliva was useful to our bodies and it prevented dehydration.
"Okay, now put it back" the teacher said while thrusting the spoon near the classmate's mouth. Everyone gasped and the kid ducked.

It was quite an experience in the 2nd period sociolgy class that morning. Our teacher later explained and made us realize that society has taught us to think that saliva or "spit" is a gross or nasty thing. It's always in our mouths, we are comfortable kissing, and sometimes sharing drinks but we would never eat our saliva from a spoon. It opened my eyes because even though I was grossed out by the thought of drinking my saliva, I couldn't really point out why it was gross in the first place. Also, the class was acting as a factor of influence for the kid who was dared to drink his spit. Before he could consider the idea, all his classmates said "ewww" and "gross!" and watched him with discusted looks. The class had confirmed to him that this was a bad idea.

But why?

We all agreed that there was n0 benefit from it, that could be part of it, but I think the point was that in our society saliva is "spit" and "spit" is gross. This is made wonder what else in my life, things I believed, was making me up as a person. The music I liked, the food I ate, the stores I shopped at, the phone I have, and may more. What makes up who you are? Are we all simply a bunch of different ideas from other people, all put together to make ourself? Can anyone really ever be considered unique?