Not intending to defend Costa but when a team clearly sets out to wind up a temperamental opponent as mercilessly as Everton did yesterday, it's unethical behaviour by the offenders as well and a miracle that he lasted on the pitch for 85 minutes. No surprise that Gareth Barry volunteered for main duties in this regard, he has one of the worst disciplinary records in Premiership history.
All this nonsense about "biting" is joyfully sensationalised by the media. If any player seriously wanted to injure another by biting you would see pieces of flesh and torrents of blood flowing from their mouths. Neither Luis, nor Costa or Lennon accomplished this (thankfully!). All that could be seen immediately afterwards was a slight reddening of the skin. Yes of course it needs to be eradicated from the game like all foul play but we are not talking about manic psychopaths here. If Costa had launched into a knee-high tackle and broken Barry's leg, I think that would warrant far greater punishment.
There would also be not much press if he'd punched him in the face, which was said when Suarez last did it too. It seems it's about what's socially acceptable and punching someone seems more so than biting.
Anyway, Barry said he didn't bite him so it's not going any further now.