I do believe that Null's logic concerning the man hate thread applies here. If you're not aware, the mods protect that thread because pretty much the entire rest of the site holds the opposite opinion, and could easily overwhelm the thread and drive out it's constituents.
So in this case, I think it's that Null feels there's so many pro-Trump people on the site, that Trump defenders seeking to push back in the thread (even those acting in good faith) would wind up vastly outnumbering the Trump haters, and turning it into a de facto pro-Trump thread.
And there is a bigger picture to that as well. Once the anti-Trump people leave, the website becomes a pro-Trump website, which inevitably turns into a circlejerk echo chamber. And when that happens suddenly there's a limit on how many people will come to the site, and Null really wants the site to grow. And I don't think this logic applies only to Trump and feminism, I'm sure if people began driving off any subgroup (like a religion, a fandom, an ideology, etc.) similar protections would be implemented.
Unfortunately, well... I think the results speak for themselves, don't they? Null is frustrated and openly wishes for a better way to ensure ideological diversity on the site. I really hope he finds it.