It's hard to be believe that people who are brave enough to deal with LGBTQIA issues in their own lives and face actual in-your-face challenges would actually give a crap what pronoun someone used on a technical forum, and it seems absurd to regulate such behavior. If I don't want to be a dick and am aware of the preference, then I will try and use the person's preferred pronoun - but I'm certainly not obligated to d…
It matters because even if you don't think it's a big deal, it can be death by a thousand papercuts for others. Seeing "he" used as a default pronoun just reminds me that people will assume I'm a man, further entrenching this idea subconsciously that people like me don't belong in tech. When I'm misgendered online, I have an internal conversation of "Do I correct them? Do I want to be perceived as not contributing to the discussion and be punished for that? Will I be seen as a crazy SJW and attacked for it?" That's a mental stress that cisgender men simply don't have to deal with.
Use gender-neutral language by default. It's not hard, and simple mistakes are forgiven. However, if one isn't willing to put the slightest amount of effort to either avoid pronouns or use the singular they, it shows they doesn't actually care about the concerns of people unlike themselves. And that shows a lot about what kind of person they are.