lets say carragher was in a bar fight, less aggro would have been made over it. If you ask me when it comes to acts of aggression spitting is way below punching. In fact its not even in the same ball park. Carragher throwing a coin into the crowd at highbury is worse than spitting for example yet the spitting thing referred to a lot
I think it's how spitting is viewed in our society.
Maybe it goes back to Victorian times? When one way to sort out differences was to roll your sleeves up and have a tear up on the cobbles. Sort of a manly thing to do.
Whereas spitting is the kind of thing that you might do once or twice as a kid, get bollocked by yer ma for doing it, and never do it again.
So the implication is that if you're caught spitting as an adult then you're either very immature or weren't raised proper.
Hence it is frowned on more than fist fighting.
It also comes across a bit low and crude if you eject your bodily fluids on someone.