I've never had a problem with urinals and I've never been able to identify with people who do, although I can understand why someone would (if that isn't contradictory). I've always been quite open with my body.
As for spitting, I believe people spit in urinals because spitting is fun and a nice release, and spitting into a drain/toilet is the best place to do it. I used to spit a lot in the shower, both to spit out the shower water and just out of habit. People probably spit at the urinal a few times for fun and then it becomes a habit and they do it just about every time.
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