By Nate Raymond (Reuters) – The U.S. Supreme Court on Monday made it harder for prosecutors to win convictions of doctors accused of running “pill mills” and excessively prescribing opioids and other addictive drugs by requiring the government to prove that defendants knew their prescriptions had no legitimate medical purpose. The 9-0 ruling, authored by liberal Justice Stephen Breyer, sided with Xiulu Ruan and Shakeel Kahn, who argued that their trials were unfair because jurors were not required to consider whether the two convicted doctors had “good faith” reasons to believe the numerous op…