“We think this rule falls far outside what is a reasonable rule of unethical because one, it conflicts with the SEC’s rule; two, it conflicts with the common law; and three, the secretary has pointed to no authority outside the state that has adopted a similar rule,” Amy M. Saharia, a partner at Williams & Connolly, argued on behalf of Robinhood, noting that Section 415 of the act in question makes clear to “make the law of Massachusetts uniform with its sister jurisdictions and the federal government.”