Generally it is very difficult to confirm intent, so most red card offences (bad tackles, or an errant elbow) have to be treated as part of the game, which are punished with a sending off and a standard ban.
Biting is completely different, it is a clear decision to cause harm to another player. Much like if someone just randomly started punching another player in the face. Fortunately in football you rarely actually see acts of violence like this and most similar offences tend to be 'handbags' rather than a physical attack (such as touching heads together, or pushing a hand into someone's face). Rarely do players seem to cross the line in the way that Suarez does.
I would say that (imo) Alex Song came close to crossing this line with his elbow, but he's not got a history of deliberately elbowing players in the back. Suarez does have a history of deliberately biting players.
Biting is completely different, it is a clear decision to cause harm to another player. Much like if someone just randomly started punching another player in the face. Fortunately in football you rarely actually see acts of violence like this and most similar offences tend to be 'handbags' rather than a physical attack (such as touching heads together, or pushing a hand into someone's face). Rarely do players seem to cross the line in the way that Suarez does.
I would say that (imo) Alex Song came close to crossing this line with his elbow, but he's not got a history of deliberately elbowing players in the back. Suarez does have a history of deliberately biting players.