If you're honestly concerned with fairness, then apply the same rules to everyone else who was wearing jeans at any point during the tournament including today. And yet so far, only
@MagnusCarlsen has been singled out.
A: FIDE did not ban Magnus from the tournament. He was not paired in round 9. He can continue tomorrow.
B: We gave Magnus more than enough time to change. But as he had stated himself in his interview - it became a matter of principle for him.
C: Rules are applicable to all the participants, and it would be unfair towards all players who respected the dress-code, and those who were previously fined.
D: The dress-code was known way before, and it was suggested by Athletes Commission, consisting of grandmasters.
Said that, I am sorry for the situation that occured - FIDE was very welcoming to Magnus and his family, and we never wanted it to explode. However I fully back a decision of the Chief Arbiter Alex Holowczak.