Fear based actions can still be sexist though. We're talking about treating people different based on their sex.
Let's draw a parallel. Most people would consider crossing the street because there is a black man walking towards you as a racist action. Sure, not burning a cross in their lawn racist, but racist nonetheless (it's a spectrum). I would argue that people that do this do so because they are afraid of said black person. Yes, their action is caused by fear, but their fear is caused by racism (i.e. they view a black person as being more likely to be dangerous than a person of another race).
Looping back, I believe you are right that these decisions are fear based, but it is fear that women are out to get you, which is the sexist part. In reality it does not appear that women are more out to get you than men are. Though we likely have a perception bias that they are because of social media. There's the double edged sword of awareness. It can help you solve a problem but it can also increase the problem because it can make you blind to the root issues.
I think this brings us to problems with social media or more precisely sensationalism (which is amplified in social media but far from the only platform that encourages this). These cases are more visible and gives us a selection bias. But I guess we have to encourage good faith discussions (which is a rule on HN btw) through media, which is rather difficult to do at a cultural level. And we don't want to entirely kill sensationalism either because topics going viral has a lot of utility (such as that more women are being open about the abuse that they've received. Yes, this does lead to a higher number of false accusations, but they still are a very small percentage of accusations). It's a really difficult problem but I think encouraging good faith arguments, being kind to one another, patience, and allowing for mistakes are a necessary step to be able to solve this entire issue (which I'm not going to pretend to have real answers). Particularly I think the last component is essential because we need to recognize that not everyone learns the same lessons. If we're going to say things like "everyone is racist" or "everyone is sexist" we have to also allow people to safely make mistakes and importantly be given the opportunity change/fix their behavior. I personally believe if people are not given this opportunity they double down on their ways. It is a coping mechanism because no one wants to be the bad guy.