They may have underlying meanings but in terms of end result punching is far worse than spitting. For god's sake we've all at least once been spat in the face by people accidentally as they talk or eat or whatever. It's quite hard to accidentally punch someone in the face, but it hurts a helluva lot more. People have died from taking just an odd thrown punch... I doubt spitting carries the same threat.
Have you never been angry on a football pitch, wanted to kick something in frustration when its not going your way? Well I have. And whilst I don't really know why he is mind went straight to gobbing a big phlegmball, I do know that that level of emotion makes it easy for you to make rash decisions. I've fallen out with mates over stpid kickabouts because I hated losing them. So I don't see the problem with giving him a wiped-clean (spitshined?) slate to start at Goodison, on the counts that a) notwithstanding the obvious stigma, spitting isn't really that bad in any way and b) he did durin a game, in the heat of the moment, not to some innocent bystander in the street when pissed. (I'm looking at you, Joey Barton. He's never spat at anyone - though he did nearly blind someone with a cigar and was charged for instigating a brawl outside the Maccies in town at 4am during a season)
It never bothered me even one tiny bit that he spat at some nomark playing for West Brom. I really can't work out how/why it irks others.
I think you might just be looking for reasons to criticise, but hey ho