Yeah, I understand entirely that it can be hurtful to those who don't want to out themselves, which I why I suggested making it hidden by default (and yeah, absolutely agree you can further support these people by making the field optional in the first place). I just think that the benefits in that it clearly supports non-binary and non-cis people is such a massive benefit that it's kinda worth it? Particularly considering how most people online try to hide links to their real life persona, so this could also be a way for people who aren't out irl to be out in a public space where it can't be linked to the "real them", a place where they can actually be themselves
For a comparison, I once ran a program where year 11/12 students would come to Monash to learn a bunch about science in general and what life as a scientist is like. I actually forbade the volunteers from using things like gender, sexuality, etc., in the getting to know you games so that the students didn't feel pressured to out themselves or lie about their own identity. However, I did let the staff (and even encouraged them) to put pronouns onto their name badges, and a few students commented on how they liked that and it made them feel safe about the environment they were in
I understand the circumstances are a bit different on a forum, where things in writing are a lot more front and center, so it may feel a lot less optional like it did in the example I gave - I just think it's a small thing that will go a long way to helping troubled students at the very least feel like this is a safe place, even if they don't want to reveal their pronouns. Hell, for extra security, you could even make it one of those fields that you don't collect at registration, and the user has to go out of their way to edit it (like with how personal text currently is - which is also how I saw this system working when I suggested it, but mentioning just so everything's clear with no assumptions)