why Hamilton's +25 sec penalty issued by race stewats Fair-Though it seems Unfair?

On Sunday 7th september Lewis Hamilton who had unofficially won the Belgian GP at SPA Francorchamps was issued an 25seconds penalty which caused him being stripped off his 10 championship points and an race win to his name.

Though the decision of stewards seemed quite unfair,especially from the point of view of hamilton fans,still legally the descision is quite fair,According to the rules-'A driver may not cut an corner until and unless the driver has an fair advantage as compared to the driver he overtook or he has already passed',but in the case of Lewis hamilton,Kimi overtook him and (lewis)had no advantage and rather he took advantage by cutting the bus stop chicane.

Hence the Stewards issued an 25sec penalty which means 25sec were added to Lewis Hamilton's race finish time hence causeing him to be third .The 25sec penalty ws given as an substitute to drive through penalty,as the incident was investigated after the race,an drive through penalty couldnt be passed.This year itself Hmilton was penalised with an drive through penalty for cutting the corner 1 at Magny-cours-France during the French GP.