Karna did dharma by standing besdes his friend. But, why was he killed in the name of standing for adharma?

that is law of nature created by god , on the fight between dharma and adharma , dharma will always wins and that is only right , no matter its karna or ravana , who ever standing on a adharma will be defeated and should be defeated , if karna stood for dharma he wont be killed. but he stood for duriyodana who always did bad deeds , that's why he got killed