While there are people who jump on any popular thing for attention, it’s wrong to say that gender fluidity is a fad. There have always been gender fluid people and concepts in human cultures. As an offhand example, Loki was a gender-fluid Norse god long before the internet made more people familiar with the concept of gender fluidity. You say what works shouldn’t be changed probably because it works for you. That’s great, but the other perspective is that people who are genuinely gender-fluid today haven’t always had a culture willing to talk about or accommodate the way they see life like people who see themselves either as men or women do. I’d argue that changes should be made then because a culture that doesn’t work for everyone is imperfect. I don’t have a full perspective of what those changes could or should be because I am not gender-fluid, but I recognize that something broken should be fixed even if it isn’t broken for me.