We agree that justices needn’t live like “monks,” but the meetings attended by Justices Antonin Scalia and Clarence Thomas organized by the Koch brothers weren’t high-minded social events. Their purpose was to solicit and direct millions of dollars from wealthy donors to influence elections.
Not only did the justices lend the prestige of their office to an overtly political event, but they also interacted directly with individuals and corporations with interests before the court, and did so in a setting whose entire purpose is to influence political outcomes.
You can read the rest of the letter, plus more letters on the same topic here.