Remember Google memo guy James Damore? Labor Relations Board just rejected his discrimination claim. Employees can express opinions and businesses have to ensure non-hostile workplaces. Damore's memo brought these into conflict. Therefore Google was within its rights to fire him.
Reasonable to say “advancing gender stereotypes” can contribute to a hostile work environment, but that highlights how components of hostile work environment include an element of subjectivity. All depends upon how one measures “hostile,” and convincing others something qualifies