Some argue that Model Rule 8.4(g) presents a constitutional issue and may violate rights to free speech. See this article for a brief summary of arguments on both sides.
“Proposed Rule 8.4(g) makes it professional misconduct for a lawyer to harass or discriminate while engaged in “conduct related to the practice of law” when the lawyer knew or reasonably should have known the conduct was harassment or discrimination. The proposed rule is constitutionally limited; it does not seek to regulate harassment or discrimination by a lawyer that occurs outside the scope of the lawyer’s practice of law.” (Report to the ABA House of Delegates, Page 8 of Report.)