Again it goes back to faith...we believe the Quran and the sunnah and all it commands is forever. And we also believe that if practiced the way it should then it will not be barbaric and unjust but only increase good and decrees evils, and that by abiding by it we will only achieve happiness and success not just in this life but eternally. However sadly today thats not the case. Which is why cases like mentioned in the op occur and people assume thats what shariah law is!