I am not sure that the punishment was Excessive. I think him being a superstar and a role model he should have thought his action through a bit more. Granted others may only get a one or two game suspension but you are talking Messi here. If he only got a one or two game suspension what would be the odds of him doing this again or being even more blatant?
It is not his fault that he is the best football player in the world. He should be treated like everybody else, just the fact that he is a star does not mean his punishment should be harder, that's not fair when in fact he is a regular part of a team in the football field. He should receive the same punishment as a regular player.
If people choose to make him a role model, it is their prerogative, but he shouldn't be punished differently.
I would not say he is the best football player in the world. I would say he is one of the best. Anyone who is like Messi or any of the other greats have always been held to a higher standard than the others on the team. Is it fair to them? Maybe not but that is one of the prices you pay for being famous.