I think "harassment" needs more harassing context around it to constitute harrasment in front of a judge. e.g. repeated, unwelcome, inappropriate, threatening.
For instance if two workers are on tea break together politely discussing gender, then I don't think it would come anywhere near harassment for one of those workers to say they were gender critical and for the other to say they were supportive of gender identity.
But now the tea break is over and they both go back to work. One of those two didn't like the other's point of view and starts shouting at them agressively and abusively. The recipient of the shouting calmly says "ok we can discuss this later, but we're on work time now". It has no effect, the shouting continues. The one being shouted at asks the other to stop. It doesn't stop. The shouter tries to recruit other workers to their cause in shouting abuse at the other one. This goes on for several days. An email campaign is started by the shouter to everyone in the office denouncing the other person's views. Management and HR get involved.
In both hypothetical made up examples above two diametrically opposing views get expressed, but clearly the context of what's happening where, how, trying to involve others, the repeated nature, agressive attitude, insults, threats, all count. There's a ton of additional factors on top of a belief that in my opinion are necessary to constitute harassment. Just expressing a belief politely I don't think on its own is harassment.