I understand you find that comment upsetting, but it's never acceptable to post personal abuse like this on HN, no matter who or what you're replying to.
The guidelines make it clear what style of participation is expected and what is off limits. If you wouldn't mind reviewing https://news.ycombinator.com/newsguidelines.html and taking the intended spirit of the site to heart, we'd be grateful.
When software doesn't provide a light theme, I can't use it at all. Thankfully websites are easy to fix with browser addons... ffmpeg documentation in particular looks so bad by default in my opinion.
You should always give the user a choice because it's usually very trivial to make a theme and saves everone trouble down the line. Finding the option to switch can still be a pain sometimes which is silly.