It's not fair.
You can't punish a guy just because of the consequences.
Tackles worse than the Shawcross one are put in every week, but don't cause serious injury.
At least what Shawcross did was an attenpt to play the ball, even if it was overly aggressive.
In some ways the challenge by the Arsenal player (Galllas?) against Bolton, immediately before Arsenal scored was worse; he was miles away from the ball and just stood on the Bolton player's ankle.