See this is the problem, the FA cannot separate the two incidents. He was supposedly spat at, then it's simple a ban for life for the supporter and the club fined heavily for their lack of stewarding and being naive to the situation. The next thing, he punches or attempts to punch a fan, if that is not justified punishment then I really haven't a clue what is.
What the FA have done here is take total sympathy with Aguero and actually felt sorry for him. Of course it's awful that he's been supposedly spat on, but they have glossed over it and let him away scot free.
The FA are absolute fucking idiots.