so Facebook, Instagram, YouTube and Reddit are all social-media, because all are ad-supported, and all are focused on user-generated content. HN is focused on user-generated content, but not ad-supported (okay, technically HN is 'advertising for YC', but in practice, the site isn't optimized to get you doom-scrolling so you click on more ads), and a website with a comment section, if it's like a blog or something where the majority of the content is generated by the website owner, isn't focused on user-generated content.
The combination of user-generated content + advertising, however, seems to create websites that will try to get their users addicted to the site, which can harm the lives of their users.